China considers the Taiwan Strait part of its "internal waters" primarily due to its "One China" policy, which asserts that Taiwan is an inalienable part of its territory.

This claim leads Beijing to view the waters around Taiwan, including the Taiwan Strait, as subject to its sovereignty.

Here's a breakdown of China's reasoning and how it conflicts with international maritime law:

China's Justification:

• "One China" Principle: China views Taiwan as a renegade province that must be reunified with the mainland, even by force if necessary. Based on this, it asserts sovereignty not only over Taiwan's landmass but also the surrounding waters.

• Domestic Law: Chinese officials argue that their domestic laws, in conjunction with the UN Convention on the Law of the Sea (UNCLOS), divide the Taiwan Strait into various maritime zones (internal waters, territorial sea, contiguous zone, and exclusive economic zone), all ultimately subject to China's "sovereign rights and jurisdiction."

• Rejection of "International Waters" Term: China frequently states that "international waters" is not a formal legal term defined by UNCLOS and that its use by other countries is a pretext to interfere in its internal affairs and threaten its sovereignty.

Conflict with International Maritime Law (UNCLOS):

The international community, largely based on the principles of UNCLOS, views the Taiwan Strait differently:

• Internal Waters: Under UNCLOS, internal waters are waters on the landward side of the baseline from which the breadth of the territorial sea is measured (e.g., rivers, lakes, and some bays). States have full sovereignty over internal waters, and foreign vessels generally have no right of passage unless bilateral agreements exist or the waters became internal waters by the drawing of straight baselines. The Taiwan Strait, being a body of water connecting two parts of the high seas or exclusive economic zones, does not typically qualify as internal waters.

• Territorial Sea: A coastal state has full sovereignty over its territorial sea, which extends up to 12 nautical miles from its baselines. However, ships of all states enjoy the right of "innocent passage" through the territorial sea, meaning passage that is not prejudicial to the peace, good order, or security of the coastal state.

• Contiguous Zone: This extends up to 24 nautical miles from the baselines, allowing the coastal state to exercise control to prevent infringement of its customs, fiscal, immigration, or sanitary laws within its territory or territorial sea.

• Exclusive Economic Zone (EEZ): This extends up to 200 nautical miles from the baselines. In the EEZ, a coastal state has sovereign rights for exploring and exploiting natural resources (living and non-living) and jurisdiction over other activities like marine scientific research. Crucially, all states, whether coastal or land-locked, enjoy the freedoms of navigation and overflight and other internationally lawful uses of the sea related to these freedoms in the EEZ.

• International Strait: While UNCLOS doesn't explicitly define the "Taiwan Strait," it lays out a regime for "straits used for international navigation." For such straits, even if they contain areas of territorial sea, the right of "transit passage" generally applies, which is a stronger right than innocent passage, allowing for continuous and expeditious passage. Given its importance for international shipping, many countries consider the Taiwan Strait to be such a strait, or at least to contain a corridor of international waters (EEZ) where freedoms of navigation and overflight apply.

The Core Conflict:

The fundamental disagreement stems from China's assertion of comprehensive "sovereignty" over the entire Taiwan Strait based on its "One China" principle, while international maritime law, particularly UNCLOS, establishes different zones with varying degrees of sovereign rights and freedoms for other states.

• China's claim that the Taiwan Strait is internal waters or subject to its full sovereignty directly contradicts the international understanding of freedom of navigation and overflight, especially within the EEZ, which makes up a significant portion of the Strait.

• The international community, particularly the United States and its allies, routinely conduct "freedom of navigation operations" (FONOPS) through the Taiwan Strait to assert the right of innocent passage and transit passage, demonstrating their rejection of China's expansive claims.

• China's attempts to impose its domestic laws and exercise police power beyond its territorial sea in the Strait are seen by many as a violation of UNCLOS and an attempt to unilaterally alter the established international maritime order.

In essence, China's stance is rooted in its political claim over Taiwan, which it then attempts to justify legally by interpreting maritime law in a way that is largely rejected by the international community.