The two Chinese vessels "openly intruded" into the waters around the Taiwan-controlled Taiping Island and stayed for 15 minutes before the Taiwanese coast guard expelled them, the force said in a statement.

The island, also known as Itu Aba, is the largest in the Spratly archipelago claimed by Taiwan, China, the Philippines and Vietnam.

The Taiwanese coast guard expressed its "strongest condemnation of this incident", saying it "once again maliciously escalates grey-zone harassment in an attempt to create a false impression of jurisdiction".

China claims Taiwan is part of its territory and in recent years has ramped up military pressure on the island democracy.

Beijing also claims most of the South China Sea.

Taiping's "prohibited" waters extend four kilometres (2.5 miles) from shore, Taiwan's coast guard said.

"China is systematically harassing Taiwan," the Ocean Affairs Council, which is responsible for the coast guard, said on X.

The latest in a series of Chinese activities in waters around Taiwan and islands under its control follows an operation to Taiwan's east, which Beijing said was in response to talks between Japan and the Philippines to draw a maritime boundary there.

The Ocean Affairs Council said Thursday's incident "also proves that what China did in the waters east of Taiwan should be dealt with as a challenge to international order; Japan-Philippines talks were just an excuse."

China called the Japan-Philippines talks "illegal" and has claimed exclusive control over the affected waters.

Taiwan has branded the Chinese operation in recent days as "provocative" and "expansionism in disguise".

Taipei has also accused the Chinese ships of "harassment" after they requested information from three passing commercial cargo ships, including their port of destination.

Meanwhile, Taiwan's coast guard said Saturday that a Chinese survey vessel had joined a coast guard ship in waters around Pratas Island in the northern part of the South China Sea.

It was "the first observed instance of Chinese coast guard and survey vessels acting in coordination to provoke Taiwan", the coast guard said.

Taiwan controls Pratas but Beijing also claims the island, along with most of the strategic waterway.