The ships entered the strait from the southwest on Wednesday, according to a short ministry statement which did not identify the vessels.

Taiwan's military "was closely monitoring the whole process and movements in our neighbouring sea and air space according to protocol to maintain regional peace and stability," it said.

US warships periodically conduct "freedom of navigation" exercises in the narrow waterway separating the Chinese mainland and Taiwan, triggering angry responses from Beijing every time.

Local media said Wednesday was the fifth time US warships traversed the strait this year.

Beijing views any ships passing through the strait as essentially a breach of its sovereignty -- while the US and many other nations view the route as international waters open to all.

China sees Taiwan as part of its territory to be reunified, despite the two sides being ruled separately since the end of a civil war on the mainland in 1949.

The US diplomatically recognises China over Taiwan but remains the island's chief military ally and arms supplier.

In April, Beijing said its navy warned off a French warship that had entered the Taiwan Strait earlier that month and lodged an official complaint with Paris.