TAIPEI (AFP) - Taiwan said a Chinese fighter jet entered its defence zone on Friday (June 19), the fourth incursion in as many days as Beijing's warplanes buzz the island with an unprecedented frequency.

The defence ministry said at least one J-10 fighter flew into Taiwan's south-western air defence identification zone (ADIZ), prompting Taipei to scramble its own jets.

"The Chinese communist aircraft left our ADIZ after we broadcast warnings to leave," the ministry said in a statement.

The ADIZ stretches beyond Taiwan's airspace and is used to give an early warning of possible incursions. China maintains a similar air defence zone.

Breaches used to be rare, but in the last two weeks, six incursions by Chinese jets have been made public by Taiwan.

The sudden uptick came after a US military plane flew through Taiwanese airspace with permission.

Beijing views democratic and self-ruled Taiwan as its own territory and has vowed to one day seize it, by force if necessary.

It has ramped up military, economic and diplomatic pressure on Taiwan since the 2016 election of President Tsai Ing-wen, who refuses to acknowledge that the island is part of "one China".

The pressure has done little to dent Ms Tsai's popularity, and she won a landslide second term in January.