China sent 22 fighter jets across the "median line" running down the Taiwan Strait on Thursday, Taipei's defence ministry said in its latest briefing on large-scale military drills conducted by Beijing's forces.

The Ministry of National Defense said "air defense missile systems" were deployed to track the jets and radio warnings were broadcast, according to an update on its website.

The median line is an unofficial but largely adhered to border that runs down the middle of the Taiwan Strait, which separates Taiwan and China.

It is rare for military jets to cross it.

Over the last two years, Beijing has ramped up military incursions into Taiwan's air defence identification zone (ADIZ).

The ADIZ is not the same as Taiwan's territorial airspace but includes a far greater area that overlaps with part of China's own air defence identification zone and even includes some of the mainland.

The vast majority of China's ADIZ flights occur off the southwestern edge of Taiwan.

But there has been a major increase in median line incursions after Beijing announced huge military drills to protest this week's visit to the island territory by US House Speaker Nancy Pelosi.

Of the 49 incursions Taiwan reported on Wednesday and Thursday, 44 involved Chinese aircraft crossing the median line.

Until recently, incursions into Taiwan's ADIZ were also relatively rare.

But that began to change about two years ago, as Beijing applied greater military pressure on Taiwan, which it regards as its territory and has vowed to one day take over.

Last year, Taiwan recorded 969 incursions by Chinese warplanes into its ADIZ, according to an AFP database -- more than double the roughly 380 carried out in 2020.

The most number of aircraft China has sent in a single day was 56, on October 4, 2021.

Before this week's military drills, Taiwan reported 626 incursions, an almost 70 percent increase on the same period last year.

The large number of sorties has put Taiwan's air force under immense pressure, and it has suffered a string of fatal accidents in recent years.