Foreign minister Joseph Wu urged Beijing to "return to the civilised international standards" after a Chinese foreign ministry spokesman said there was no so-called median line in the Taiwan Strait "as Taiwan is an inseparable part of Chinese territory".

Wu told reporters: "The median line has been a symbol of preventing military conflicts and maintaining peace and stability in the Taiwan Strait for many years. The Chinese foreign ministry's comment is equivalent of destroying the status quo."

"I call on the international community to condemn the CCP for its dangerous and provocative words and deeds threatening peace... China must back off," he added in a tweet.

China considers Taiwan part of its territory, to be absorbed into the mainland, by force if necessary, even though it has been self-ruled for more than seven decades.

Beijing has ratcheted up pressure on the democratic island since the 2016 election of President Tsai Ing-wen, who rejects its view that Taiwan is part of "one China".

Last year, Taiwan accused China of violating a long-held tacit agreement after its fighter jets -- for the first time in years -- crossed the median line of the waters that separate the two sides.

Washington's increased outreach to Taiwan under President Donald Trump has become yet another flashpoint with Beijing, as the US and China clash over a range of trade and security issues, as well as the coronavirus pandemic.

In recent months Taiwan has reported a sharp rise in incursions by Chinese warplanes into its air defence identification zone (ADIZ).