More than 30 Chinese warplanes entered Taiwan's air defence zone over the course of about six hours, the island's defence ministry said Thursday, a sharp ramp-up in single-day incursions by China's military.

China claims self-ruled Taiwan as its territory and has vowed to take it one day -- by force if necessary.

In recent years, Beijing has intensified aerial incursions into the island's air defence identification zone -- nearly doubling the air sorties in 2022 compared to the year before.

Taiwan's Ministry of National Defence spokesman Sun Li-fang announced Thursday that from 5 am local time (2100 GMT), "a total of 37 Chinese military aircrafts" entered Taiwan's southwestern ADIZ.

"Some continued... towards the Western Pacific for long-range reconnaissance training," Sun said at around 11 am.

While not the largest number of incursions this year -- that would be 45 sorties on April 9 -- Thursday's surge occurred over a much more compressed time frame.

Taiwan's ADIZ is much larger than its airspace, overlaps with part of China's ADIZ and even includes some of the mainland.

Taiwan's military is "monitoring the situation closely", the ministry said on Twitter, adding that patrol planes, naval vessels and land-based missile systems have been dispatched in response.

They did not clarify if the incursions were ongoing.

Analysts say China's increased probing of Taiwan's defence zone is part of wider "grey-zone" tactics that keep the island pressured.

The incursions came a day after the United States, the Philippines and Japan completed their first-ever joint coastguard drills in the flashpoint South China Sea -- which Beijing claims almost entirely.

A surge in warplanes and naval exercises by China's military around Taiwan usually coincides with Taipei making diplomatic engagements with other countries.

China lashes out at any diplomatic action that appears to treat Taiwan as a sovereign nation and has reacted with growing assertiveness to any joint military exercises around the island or visits by Western politicians.

In April, Beijing conducted three days of military exercises simulating a blockade of the island in response to Republican House Speaker Kevin McCarthy and Taiwan's leader Tsai Ing-wen meeting in California.