China may not invade Taiwan, but rather blockade it. How would this work, and could it be effective?

US officials believe Chinese President Xi Xinping has set a deadline for his military to be capable of invading Taiwan by 2027 – the centennial anniversary of the founding of the People’s Liberation Army (PLA).

US Secretary of Defense Pete Hegseth mentioned this date at a security conference in Singapore in May, warning of the “imminent threat” China poses to Taiwan.

The PLA has invested heavily in expanding and modernising its operations in recent years. Since 2015, it has built the world’s largest navy and coast guard.

But rather than threaten an invasion of Taiwan, China seems increasingly likely to pressure the self-governing, democratically ruled island with an extended blockade to force it to capitulate.

In preparation for such a possible action, China has developed a new command structure enabling it to coordinate its air, sea and land-based weapons systems to enact a strategy of lianhe fengkong (联合封控), or joint blockade. This would effectively cut Taiwan off from the outside world.

In late July, the Centre for Strategic and International Studies (CSIS) produced a report on 26 simulated war games it conducted to determine what a Chinese blockade of Taiwan would look like.

Taiwan’s natural gas supplies were predicted to run out after ten days of a blockade. Coal and oil supplies would run out in a matter of weeks. If Taiwan’s electricity was reduced to 20% of its pre-blockade levels, all manufacturing would cease. Casualties were expected to be in the thousands.

Taiwan is particularly vulnerable to a blockade. It relies more than any other developed nation on port calls relative to the size of its economy. Its biggest ports are on its west coast, facing mainland China. The island also has limited emergency food and fuel reserves.

What is a blockade under the law?

Imposing a naval blockade during armed conflict is an established right under customary international law. Blockades are not illegal per se, but they must comply with the laws of war. It’s a complicated and controversial area of the law.

To be legal, a blockade must first be effective. That is, the blockading power must maintain a force that prevents access to the enemy’s coast.

Other nations must be notified of the instigation of the blockade and its geographical extent.

A blockade must be enforced impartially against all vessels, except neutral vessels in distress. Any vessel breaching the blockade would be subject to being stopped, captured or fired upon.

Lastly, a blockade cannot prevent access to neutral ports or the delivery of humanitarian assistance to civilians.

Blockade strategies

China may use one of several blockade strategies against Taiwan. In contrast to an invasion, blockades can be scaled up or back, or reversed, depending on the unfolding security situation.

For instance, China may attack merchant shipping vessels seeking to enter Taiwanese waters to deliver essential cargo, coercing Taiwan to submit to China’s takeover. This is known as a kinetic blockade.

Alternatively, it may implement its preferred strategy of “winning without fighting”. Given the sheer size of its navy, coastguard and maritime militia, China could simply encircle the island and block access to its ports.

This could isolate Taiwan from the global economy to the point of forcing it to surrender, or weaken it sufficiently to enable an invasion, without engaging in open hostilities. This is a non-kinetic blockade.

Other ways of impeding naval passage

China may also use measures that fall short of a blockade, but have similar effects. It has passed a suite of domestic laws that legitimise military and non-military aggression of this kind.

For example, the navy or coast guard may:

• lay mines in the sea without declaring a formal blockade
• establish maritime danger or exclusion zones for foreign ships, and
• intercept, detain and regulate foreign vessels.

These tactics would only be effective because China’s domestic laws have exploited ambiguities in jurisdiction over its surrounding waters.

For example, China has passed laws requiring notification from foreign vessels if they enter waters it considers its own and under its control, and allowing its ships to alter or suspend maritime traffic for security or military purposes.

Those powers, however, are inconsistent with international law. China, for example, considers the Taiwan Strait as Chinese territory. Under the UN Convention on the Law of the Sea, however, the strait is considered international waters, which enables freedom of navigation for all vessels.

Also, creating an unstable security environment around Taiwan (similar to what Houthi forces have done in the Red Sea), or threatening penalties and sanctions for failing to comply, may in effect be tantamount to a blockade.

How to counter a blockade

It is not clear how other nations would respond to a Chinese invasion or blockade.

In recent years, China has attempted to project its naval power by establishing no-go zones in its neighbourhood, such as turning the South China Sea into its own fortified waters.

One way to oppose China, then, would be a counter-blockade. This would entail allied naval forces, likely led by the United States, closing the choke points, such as the Malacca Strait, on which Chinese seaborne trade with global markets depends.

However, counter-blockades are problematic, too. The impact on the world economy would be huge, as a blockade of the Malacca Strait, for example, could impact all trade between Asia and the rest of the world. China has also stockpiled domestic resources and expanded its land-based trade routes in recent years.

The best option, then, might be supporting Taiwan to survive a long blockade, forcing China to back down.

This means helping Taiwan become more resilient by increasing its food, fuel and medicine stockpiles, developing robust communication and cyber defences, and strengthening its port and energy infrastructure.

If the US built up its naval capacity in the Pacific, it could also use frigates to escort convoys of merchant ships to break a Chinese blockade, though the CSIS war games indicated this could come at a considerable cost of lives and ships – and increase the potential for all-out war.