The destroyers USS Mustin and USS Benfold sailed into the narrow waterway separating Taiwan and China on Saturday morning and were expected to continue on a northeast course, Taiwan's defence ministry said in a statement.

"The military is monitoring the situation in neighbouring areas, and has the confidence and abilities to maintain regional stability and defend national security," the statement added.

A defence ministry official told AFP the ships were still in the strait on Saturday night, sailing in what he described as international waters.

The warships' entry into the strait comes as Washington and Beijing are locked in a trade war and as tensions escalate between Beijing and Taipei.

US President Donald Trump on Friday rolled out 25 percent tariffs on $34 billion of Chinese goods in what Beijing called the "largest trade war" in economic history.

China said it was hitting back with retaliatory measures on US goods but did not immediately providing precise details.

China sees self-ruling democratic Taiwan as part of its territory to be reunified, by force if necessary but the island sees itself as a sovereign country.

The two sides split in 1949 after a civil war.

Although the US does not have official diplomatic relations with Taiwan, it is its most powerful ally and biggest arms supplier.

China has stepped up diplomatic and military pressure on Taiwan since Beijing-sceptic President Tsai Ing-wen took office two years ago as her government refuses to acknowledge that the island is part of "one China."

Beijing has staged a string of military exercises, including a live-fire drill in Taiwan Strait in April, which it said were aimed at Taiwan's "independence forces".

It has lured away four of Taiwan's diplomatic allies since Tsai came to power, leaving only 18 countries in the world that recognise Taipei over Beijing.

A growing number of international airlines and companies were also forced to change Taiwan's name to "Taiwan, China" or "Chinese Taipei" due to pressure from Beijing.

Tsai has criticised China for attempting to change the status quo between the two sides and urged the world to "constrain" its ambitions.

Beijing is also incensed by the recent warming relations between the US and Taiwan, after President Trump signed legislation paving the way for mutual visits by top officials and the US government approved a licence required to sell submarine technology to Taiwan.