China To Quarantine Taiwan

China has significantly increased pressure on Taiwan in recent years, stoking fears that tensions could erupt into outright conflict. Much attention has been paid to the threat of an invasion, but Beijing has options besides invading to coerce, punish, or annex Taiwan. One major step China could take is a “gray zone” quarantine led not by its People’s Liberation Army (PLA) but by its coast guard and other law enforcement forces. Rather than sealing off the island, a quarantine would aim to demonstrate China’s ability to exert control over Taiwan. A quarantine is more feasible for China and more likely than an invasion or blockade in the near term; it also presents unique challenges in terms of how Taiwan and the international community can respond. This brief explores two hypothetical maritime quarantine scenarios that are informed by in-depth research, tabletop exercises, private consultations, and expert surveys conducted by the CSIS China Power Project.

Introduction

China has significantly increased pressure on Taiwan in recent years. China’s military frequently flies aircraft within the island’s air defense identification zone (ADIZ) and across the Taiwan Strait median line. In August 2022 and April 2023, China escalated in response to U.S.-Taiwan political engagements by staging unprecedented large-scale military exercises around Taiwan. China has also deployed its navy and coast guard in increasing numbers around Taiwan and its outlying islands.

Cross-Strait tensions further intensified in the wake of William Lai’s inauguration as Taiwan’s president on May 20, 2024. Three days after Lai delivered his inauguration address, China commenced two days of large-scale military exercises surrounding Taiwan, called “Joint Sword-2024A,” and accompanied them with “comprehensive law enforcement operations” (综合执法演练) involving China’s coast guard. Chinese officials stated that the drills were intended to “serve as a strong punishment for the separatist acts of ‘Taiwan independence’ forces and a stern warning against the interference and provocation by external forces.”

These Chinese escalations against Taiwan are raising concerns that Beijing could take even more significant steps to “punish” and coerce Taiwan going forward. One major action China could take against Taiwan is a gray zone quarantine of the island. Quarantine scenarios have received far less attention than other contingencies, such as an invasion, but a quarantine is likelier in the near term and therefore warrants increased scrutiny.

What Is a Quarantine?

The term quarantine is sometimes used interchangeably with “blockade.” However, this report differentiates between the two, defining a quarantine as a law enforcement–led operation to control maritime or air traffic within a specific area while a blockade is foremost military in nature. A quarantine would entail China’s coast guard and other forces conducting gray zone operations intended to stay below the threshold of an armed conflict. Thus, the military would play a supporting role — not a leading role — in such operations.

The political and operational goals of a quarantine are not to completely seal Taiwan off from the world but to impose a system of controls over the island’s maritime and/or air commerce. In a quarantine, key necessities like food and medicine could continue to flow into Taiwan, enabling China to assert that its law enforcement operation is imposing no hardship. A quarantine could target the delivery of specific goods, such as shipments of U.S. weapons to Taiwan, but such a move would risk provoking a more direct U.S. response.

A key goal of the quarantine approach is to obtain compliance from international companies and other countries to demonstrate China’s power over Taiwan. This is similar, in some respects, to China’s 2013 declaration of an ADIZ over much of the East China Sea. Many airlines, including U.S. companies, complied with Beijing’s demands then.

A quarantine of Taiwan could involve a change of Chinese domestic policy to establish new rules or requirements for regulating trade or traffic into Taiwan, or it could simply involve Chinese law enforcement forces stepping up activities against Taiwan on the basis of existing laws. Thus, a quarantine would focus on forcing compliance with Chinese rules and strengthening China’s asserted sovereignty claims over Taiwan.

In contrast to law enforcement–led quarantines, this brief defines a blockade as a military-led operation. China’s PLA would be leading a blockade by encircling parts or all of Taiwan, while forces such as the coast guard and maritime militia play a supporting role. More intense versions of a blockade could involve missile strikes against Taiwan as well as mining of waters around Taiwan.

A blockade would, by nature, involve much more escalatory operations than a quarantine. A quarantine would not intentionally involve the use of kinetic force to attack targets, though it is possible that escalation could lead to an exchange of kinetic attacks.

There are no publicly available doctrinal writings on how exactly China could execute a quarantine. However, China has conducted several maneuvers and exercises that are indicative of how it can use law enforcement operations to assert control over traffic to Taiwan and complicate Taiwan’s maritime environment.

In August 2022, when then speaker of the house Nancy Pelosi visited Taiwan, China’s Maritime Safety Administration (MSA) deployed a large patrol vessel, the Haixun 06, to conduct operations off the coast of China’s Fujian Province and in the Taiwan Strait for the first time. In April 2023, after Taiwan’s president Tsai Ing-wen transited through the United States, the Haixun 06 deployed again. This time, it sailed farther into the Taiwan Strait, and the Fujian Province MSA announced that the vessel would carry out “on-site inspections” of vessels, though there were no reports that inspections occurred.

More recently, China increased coast guard patrols near Taiwan’s outlying Kinmen Islands after an incident there. In February 2024, a Taiwan coast guard vessel chased and collided with a Chinese vessel that Taiwan asserts was illegally fishing near Kinmen. The incident resulted in the death of two crew members. China responded by increasing coast guard patrols near what Taiwan calls “restricted” and “prohibited” waters around Kinmen. At one point, Chinese coast guard personnel boarded a Taiwan-owned tourist boat to check its licenses and paperwork.

Amid this uptick in activity around Kinmen, China conducted a series of combat activities in which naval and air forces from the PLA Eastern Theater Command conducted drills jointly with the China Coast Guard (CCG). Chinese official outlets described the exercises as simulating “emergency scenarios” and focusing on enhancing forces’ “interoperability and joint strike capabilities.”

China again stepped up the involvement of the CCG in May 2024 during its latest round of large-scale exercises around Taiwan. Alongside the PLA exercises, the CCG conducted its own operations around two of Taiwan’s outlying islands. On the same day that the PLA exercises started, the Fujian Province Coast Guard launched a “comprehensive law enforcement exercise” in waters around Wuqiu and Dongyin “to test its joint patrol, rapid reaction and emergency response capabilities.” The CCG indicated that its patrol vessels came as close as 2.8 nautical miles from Wuqiu’s islands and as close as 3.1 nautical miles from Dongyin, marking the first time CCG vessels have entered waters there.

In addition to patrolling around Taiwan’s outlying islands, four CCG vessels sailed east of Taiwan and another three sailed southwest of Taiwan near the southern entrance of the Taiwan Strait. As part of the exercises east of Taiwan, videos released by official Chinese outlets showed multiple CCG ships encircling a target vessel and spraying water cannons, though the vessel appeared to be Chinese-flagged, and the video did not show the water cannons actually hitting the vessel. This represents a marked increase in intensity compared to previous CCG activities around Taiwan, and it is the latest and clearest indication that China is preparing its law enforcement and military forces to operate together in the context of a Taiwan Strait crisis.

Why China Might Quarantine Taiwan

A quarantine of Taiwan would represent a substantial escalation of coercion against the island, but it offers China several distinct advantages. First, a quarantine allows China to impose greater political and administrative control over Taiwan. China’s efforts to restrict air or maritime traffic to the island could allow Beijing to assert its sovereignty claims and demonstrate that Taiwan does not have control over its own claimed sovereign space. This could undermine Taipei’s ability to self-govern and erode the Taiwan public’s confidence in Taiwan’s military and coast guard.

Second, China could use a quarantine to intervene in Taiwan’s domestic politics by imposing economic costs on the island. If the disruptions stemming from a quarantine are sustained for a lengthy period, elements within Taiwan’s society could leverage this to portray Taiwan’s leaders as ineffective. This could either lead to a loss of public support for Taipei or increase political pressure on Taiwan’s leaders to negotiate or improve relations with Beijing.

Third, a quarantine is more limited in scope than a blockade or other large military operations. A quarantine led by China’s coast guard is not a declaration of war against Taiwan. Because a quarantine is not overtly PLA-led, there is a lower risk that escalation will lead to direct military confrontation. If the quarantine is cast as a law enforcement operation, China can easily announce the end of the operation and claim its objectives were met. Relatedly, China could choose to target only certain types of products, or the quarantine could be scaled to cover all air and maritime flows to Taiwan.

If China successfully conducts a limited quarantine, it would set a political precedent and establish a new normal of Chinese activity, setting the stage for it to carry out more expansive operations in the future. The unprecedented scale and complexity of a quarantine operation would also provide a valuable opportunity for Chinese law enforcement, maritime militia, and the PLA to train and test their capabilities and identify weaknesses for subsequent operations.

Fourth, a quarantine could have impact without full and sustained implementation. Although China has significant capabilities to use law enforcement and other assets to physically disrupt trade to Taiwan, it may only need to demonstrate intent and some capability for the quarantine to be effective. The announcement of a change in Chinese policy — or the beginning of law enforcement actions — is likely to have a chilling effect on the willingness of businesses to invest or operate in Taiwan. Similarly, demonstrated Chinese willingness to search and seize only a handful of commercial ships could have an outsized deterrent impact and discourage similar transgressions.

Many commercial airlines and shipping companies are likely to comply with Chinese pronouncements. Even if some shipping companies do not comply with quarantine regulations, adherence by most of them would significantly strengthen China’s narrative that it has control over Taiwan.

Finally, China’s use of the coast guard and civilian law enforcement complicates the ability of the United States and regional actors to respond. A quarantine does not require closing off or restricting international traffic through the Taiwan Strait — an action that other countries could use as a justification to intervene to assist Taiwan and defend international legal rights to freedom of navigation.

The United States also does not have sufficient coast guard forces forward deployed to the Indo-Pacific to respond in kind. The United States could lean on other forward-deployed forces, including air and maritime assets, to help Taiwan respond, but it is likely to be cautious to avoid the optics of using “gray-hulled” U.S. Navy vessels to confront “white-hulled” CCG vessels.

In a recent survey of experts from the United States and Taiwan, the China Power Project found that most are skeptical of U.S. and allied willingness to intervene in a quarantine. Only 13 percent of surveyed U.S. experts and 9 percent of Taiwan experts were “completely confident” that the United States would intervene militarily to defend Taiwan from a quarantine. An even smaller percentage had confidence that allies and partners would support a U.S.-led multinational military intervention.

China’s Ability to Quarantine Taiwan

A quarantine would be an immense and unprecedented undertaking for China, requiring it to overcome complex logistics hurdles and jointly command law enforcement, maritime militia, and military forces. Nevertheless, China has immense capabilities at its disposal that would enable it to conduct a quarantine.

With over 150 oceangoing vessels and more than 400 smaller vessels at its disposal, the CCG is the largest coast guard in the world. The CCG is a quasi-military organization that reports to China’s highest military authority, the Central Military Commission. Many CCG ships were transferred from the navy and still carry some military-grade weapons, such as 76 mm cannons.

Taiwan’s coast guard would be at a major quantitative and qualitative disadvantage. It has just 10 oceangoing ships and approximately 160 smaller vessels. These vessels are responsible for protecting the over 300 harbors and ports on Taiwan’s coast and for law enforcement activity within 24 nautical miles of the island.

China’s MSA, which is the primary non–coast guard civilian agency responsible for maritime security and navigation, would work alongside the CCG to lead a quarantine. The MSA’s fleet consists of at least three dozen oceangoing vessels and hundreds of smaller patrol craft.

In addition to the CCG, China also possesses a large maritime militia: a force of organized, trained, and armed personnel aboard fishing vessels and other craft. These vessels operate under the official guise of commercial fishing activity, but in actuality, they work in tandem with China’s law enforcement and under the shadow of the PLA to support Chinese maritime operations. Because the maritime militia is not officially a law enforcement or military entity, it is challenging for other countries to respond to its activities.

There is little information about the full size of the maritime militia, but some estimate that it consists of more than 100 large vessels and as many as 3,000 smaller vessels. The lion’s share of the maritime militia is concentrated in the South China Sea, where militia vessels often swarm by the dozens or hundreds to defend China’s territorial claims in the region.

It is unclear how many Chinese maritime militia operate near the Taiwan Strait, but those that would be involved in a Taiwan contingency may be based at ports in China’s Fujian, Zhejiang, Jiangsu, and Shandong Provinces. Meanwhile, Taiwan does not have an equivalently large force similar to China’s maritime militia. This means Taiwan would largely need to lean on its coast guard to respond to militia activity.

Finally, China’s military forces also significantly overshadow Taiwan’s. As of 2023, the PLA Navy comprises a battle force of over 370 vessels, many of which are based in areas close to the Taiwan Strait. The PLA Air Force and Navy also boast thousands of aircraft, which support China’s ability to project power and conduct intelligence, surveillance, and reconnaissance (ISR) around Taiwan. If the situation around Taiwan goes kinetic, Taiwan would face a much larger force than its own, limiting its ability to effectively respond to aggressive Chinese activities.

The Role of Geography

Geography is a major factor at play in a quarantine scenario. At its narrowest point, the Taiwan Strait is only about 130 km (81 miles) wide, meaning China does not have to deploy forces at long distances from China’s own shores.

Adding to Taiwan’s exposure is the fact that the island has only a handful of major international ports. Most of the busiest ports — including Kaohsiung, Taichung, Taipei, Keelung, and Mailiao — are also the closest to mainland China. There are two less-busy ports — Hualien and Su’ao — on Taiwan’s east coast, as well as additional smaller harbors.

The Port of Kaohsiung stands out among these. In 2022, an estimated 57 percent of Taiwan’s maritime trade entered through the Port of Kaohsiung, making it an indispensable commercial hub for the island. It is by far Taiwan’s busiest port for containerized goods and oil, and the nearby Yung-An Liquefied Natural Gas (LNG) Terminal is Taiwan’s largest facility for importing LNG.

All of this means it is easier for Chinese forces to reach Taiwan’s most important shipping ports. In fact, if China can effectively control traffic into just one port, Kaohsiung, it can achieve significant influence over what gets into Taiwan.

How China Could Implement a Quarantine

The scenarios outlined below are only two examples of potential maritime quarantines. There are many other conceivable approaches China could take, but these scenarios align with activities and capabilities China has demonstrated through past operations.

Scenario 1: Limited Maritime Quarantine

In this first scenario, Beijing leverages its law enforcement forces to conduct a limited maritime quarantine of some of Taiwan’s ports. This is not aimed at choking off Taiwan’s access to trade, but a gray zone operation to achieve more limited — but still significant — objectives.

Days or weeks before the start of quarantine operations, China readies maritime law enforcement forces within its coast guard and MSA. Beijing also mobilizes portions of its military and calls up maritime militia fishing vessels in the area.

China begins by publicly announcing “enhanced customs inspection rules.” It avoids using terms like “quarantine” or “blockade” to describe its actions. In order to enter Taiwan, all cargo and tanker vessels must file advance customs declarations with relevant Chinese authorities.

Chinese law enforcement vessels will be authorized to board vessels, conduct on-site inspections, question personnel, and undertake other measures against noncompliant ships. Chinese authorities also threaten fines and market access restrictions for companies flouting the new rules.

The quarantine is set to enter into force 48 hours after announcement. This allows China time to deploy forces into position after they have been mobilized. It also allows shipping companies with vessels in transit warning time to comply, lending some credibility to China’s actions.

Chinese authorities do not announce a specific location for the inspections, but they intend to target the Port of Kaohsiung, Taiwan’s busiest port. China positions more than 10 law enforcement patrol vessels off the coast of Kaohsiung. China also deploys a smaller contingent of law enforcement vessels within the Taiwan Strait off the coast of other major ports at Taichung and Taipei. About 48 hours after the initial announcement, Chinese authorities issue notices that enforcement is beginning and that its patrol ships will stop noncompliant vessels.

The vessels intrude into Taiwan’s 24-nautical-mile contiguous zone and occasionally approach the 12-nautical-mile territorial seas boundary. This is symbolically important since China does not recognize Taiwan’s claims to these boundaries. During large-scale military exercises around Taiwan in April 2023, several PLA vessels intruded into Taiwan’s contiguous zone in a maneuver intended to delegitimize Taiwan’s claims.

Supporting these law enforcement vessels are approximately 20 maritime militia fishing vessels extending along Taiwan’s contiguous zone. These maritime militia vessels are not authorized to conduct boarding or search operations against commercial vessels. Instead, they fill in gaps in ISR and complicate Taiwan’s maritime domain awareness by swarming in certain areas. China could deploy significantly more militia forces — as it has done in the South China Sea — but the militia forces are not as well trained as the coast guard, and Beijing may worry about their discipline and ability to face off against Taiwan’s coast guard.

While this quarantine is ostensibly a law enforcement operation, the military plays a key supporting role. China’s navy deploys five surface action groups (SAGs) to encircle Taiwan from a distance. Each SAG comprises three to six ships — including destroyers, frigates, support vessels, and covertly deployed attack submarines — for a total of nearly 30 warships. They are primarily meant to deter intervention by foreign coast guard or military forces and to respond if Taiwan’s navy escalates or attempts to escort vessels into the island. They also provide ISR, extending China’s air and maritime domain awareness farther into the Pacific, helping Beijing monitor U.S., Japanese, or other movements. In addition to naval operations, the PLA constantly flies sorties of manned and unmanned aircraft around Taiwan to monitor traffic.

Beijing does not need universal compliance with the customs rules in order to claim success. Compliance by around 75 percent of shipping companies would be a considerable success for China.

Chinese-flagged shipping vessels — which account for a significant share of the total traffic — universally comply with Chinese authorities, and Beijing permits them to enter Taiwan’s ports. Beijing counts on most foreign shipping companies complying with the “enhanced customs rules” to avoid reprisals, but several companies headquartered in Taiwan, the United States, and certain other countries publicly oppose and disregard the rules. Over the course of one week, Chinese law enforcement vessels only stop and search one or two vessels in total and focus solely on Taiwan-owned vessels.

If China meets relatively limited pushback and most companies comply with Chinese customs rules, China begins to draw down operations after about one week. However, a considerable law enforcement and military presence persists around Taiwan in the weeks that follow — an indication of the new normal China has established.

Scenario 2: Full Maritime Quarantine

This scenario is a significantly scaled-up version of the first scenario. Like the first scenario, China declares new “enhanced customs inspection rules” that will require advance notice with Chinese authorities to ship goods into Taiwan.

This time, however, China publicly announces a quarantine area covering the entire island of Taiwan. The zone extends 24 nautical miles from Taiwan’s territorial baseline, matching with Taiwan’s claimed contiguous zone. This is intended to delegitimize the contiguous zone and demonstrate China’s willingness and capability to impose its will in an area ostensibly under Taipei’s jurisdiction.

Chinese authorities announce that the inspection regime will go into effect 48 hours after declaration. China will require the shipper of any cargo destined for Taiwan to file advance notice with Chinese customs and law enforcement officials.

China again deploys law enforcement vessels to lead the quarantine, but this time it sends a much larger overall contingent. The greatest concentration, consisting of more than 10 coast guard and maritime safety vessels, is positioned off the coast of Kaohsiung. It also deploys a dozen vessels off the west coast ports of Taipei and Taichung and sends nine near the northern Port of Keelung — Taiwan’s second-busiest import hub. Finally, it sends another six to the smaller eastern ports of Hualien and Su’ao.

This deployment of more than three dozen law enforcement vessels amounts to an unprecedentedly large maritime operation for China. It would constitute approximately one-fourth of China’s oceangoing CCG and MSA fleet.

Roughly 40 maritime militia vessels also swarm Taiwan’s coastal waters, along the contiguous zone, to fill in gaps between law enforcement vessels. As in the limited quarantine scenario, the maritime militia vessels do not participate in conducting boarding and inspecting activities. They focus primarily on conducting ISR for China and complicating Taiwan’s maritime domain awareness.

As in the limited quarantine scenario, China’s navy deploys five SAGs to extend China’s ISR, intimidate Taiwan, and deter U.S. and other forces that may try to intervene. PLA aircraft also fly regular sorties to conduct ISR around Taiwan. This time, China supplements its naval deployment by positioning the Shandong aircraft carrier and its strike group southeast of Taiwan. It launches frequent sorties of J-15 fighters east of Taiwan, repeating operations that the PLA exercised in recent years.

In this scenario, China is much more active in terms of boarding and searching vessels. Chinese forces stop at least one or two vessels per day for the period of the quarantine, focusing mostly on Taiwan-flagged ships. There also appear to be inspections of vessels belonging to some of the dozen countries that still maintain official diplomatic relations with Taiwan.

Chinese forces seize several noncompliant ships and impound them at nearby ports within China. Commercial vessels that have filed the appropriate paperwork and had their requests approved are allowed into Taiwan. However, due to heightened uncertainty about the nature of China’s enforcement, many shipping companies choose to delay their shipments, causing a significant and noticeable decline of merchandise trade into Taiwan.

As the operation stretches into multiple days, Chinese ships and personnel need to be rotated. After the large initial deployment, China can fluctuate the number of forces depending on factors like capacity, the level of compliance with the quarantine, Beijing’s desired intensity, and U.S. military posturing, if any.

These operations continue at varying levels for over two weeks before beginning to wind down. However, a significant CCG and PLA presence continues to operate indefinitely around Taiwan at a greater level than before the quarantine.

Conclusion

For both these maritime scenarios, Beijing’s goal is not to hermetically seal off Taiwan. Instead, these campaigns are designed to punish Taiwan, assert Beijing’s claimed sovereignty over the island, test the response from international shipping companies, and put significant pressure on Taiwan.

While China has the capabilities to successfully execute these and other quarantine variations, these would require operations that are far more complex than anything China has demonstrated to date. Such moves would carry significant risk for China, and its success would depend to a large degree on how Taiwan, the United States, and others respond.

Even if successfully implemented, there are limits to what a quarantine can achieve. If Beijing’s goal is to inflict enough pain to force Taiwan’s surrender, China would need to move beyond the gray zone into overt military action. A military blockade would be a key option for China if it seeks to forcefully unify Taiwan without launching an all-out invasion.

Bonny Lin is a senior fellow for Asian security and director of the China Power Project at the Center for Strategic and International Studies (CSIS) in Washington, D.C.

Brian Hart is a fellow with the China Power Project at CSIS.

Matthew P. Funaiole is vice president of the iDeas Lab, Andreas C. Dracopoulos Chair in Innovation, and senior fellow of the China Power Project at CSIS.

Samantha Lu is a research assistant with the China Power Project at CSIS.

Truly Tinsley is a program manager with the China Power Project at CSIS.