Taiwan says it deployed fighter jets to warn off 30 warplanes sent by China into its air defence zone.

Taiwanese F16 aircraft prepare to take part in a drill aimed at being ready to meet any incursion into their air defence identification zone. Photo: AFP

The incident on Monday marked the biggest incursion since January.

It came days after US President Joe Biden warned China against invading Taiwan, and on the same day as a US official visited the island to discuss security with leaders.

China has ratcheted up the frequency of its air missions in recent months, claiming they are training drills.

Such moves have angered Taiwan and increased tensions in the region.

China sees Taiwan as a breakaway province, which it can take by force if necessary.

The latest incident included 22 fighters, as well as electronic warfare, early warning and antisubmarine aircraft, Taiwan's defence ministry said.

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The aircraft flew in an area to the northeast of the Pratas Islands that is part of the Taiwan's air defence identification zone (ADIZ), according to a map the ministry provided.

But the planes did not cross over into Taiwan's airspace itself, which would have been regarded as an act of hostility.

An ADIZ is an area outside of a country's territory and national airspace but where foreign aircraft are still identified, monitored, and controlled in the interest of national security. It is self-declared and technically remains international airspace.

Taiwan has been reporting for more than a year that Chinese aircraft have been flying into its ADIZ, calling it "grey zone" warfare aimed at testing their military response and wearing them out.

Analysts have previously said the incursions were a warning against Taiwan's government from moving towards a formal declaration of independence.

Beijing has said in the past that the exercises were geared to protect its sovereignty.

Biden referred to the air incursions during his visit to Asia that concluded last week - his first visit to the region as president.

He said China was "already flirting with danger right now by flying so close" to Taiwan, and issued his strongest warning to China yet, saying the US would be willing to respond militarily if Beijing were to invade the island.

His words appeared to mark a shift from the US' longstanding policy of "strategic ambiguity" on Taiwan, which allowed the US to remain deliberately vague about its response in such a situation.

China's military said last week it had recently conducted an exercise around Taiwan as a "solemn warning" against its "collusion" with the United States.

Monday's incursion took place as US senator Tammy Duckworth arrived in Taipei on an unannounced visit to discuss matters of regional security and trade with Taiwanese president Tsai Ing-wen.