Tensions between Beijing and Washington have soared over the fate of democratic self-ruled Taiwan, which China has vowed to one day retake, by force if necessary.

A group of American lawmakers arrived on the island Thursday offering support for the Taiwanese authorities, who Beijing accuses of seeking independence for the island.

In response, the Chinese army on Friday carried out "a naval and air force combat readiness patrol in the direction of the Taiwan Strait," a spokesperson for the Eastern Theater Command said in a statement.

"This is a necessary measure in response to the current situation in the Taiwan Strait," they added, pledging the army would "protect sovereignty and territorial integrity of the nation."

"The army will continue to be on high alert and take all necessary measures to counter, at any time, any interference by external forces and any conspiracy by separatists aiming at the so-called 'Taiwan independence'."

No other information about the drills was given.

China's foreign ministry on Friday expressed Beijing's "firm opposition" to the US lawmakers' visit, the second by members of Congress to the island this month.

Led by Mark Takano, chairman of the House Committee on Veterans' Affairs, the delegation met with Taiwan's President Tsai Ing-wen Thursday in a show of support for a rare issue on which there is cross-party consensus in the US.

"Taiwan will continue to step up cooperation with the United States in order to uphold our shared values of freedom and democracy, and to ensure peace and stability in the region," Tsai said.

China has intensified pressure on Taiwan since the 2016 election of Tsai, whose party has long advocated for the island's self-rule.

Beijing baulks at any use of the word "Taiwan", or any references to the island as a "country" and diplomatic gestures that might lend a sense of international legitimacy to the island.