Taiwan's defense authorities say more than 20 Chinese military aircraft have crossed the so-called median line on the Taiwan Strait, following US House Speaker Nancy Pelosi's visit to Taiwan.

The authorities say 27 Chinese fighter aircraft approached airspace near Taiwan on Wednesday and 22 of them crossed the median line.

It is rare for such a large number of Chinese warplanes to be confirmed to have entered Taiwan's side of the line in one day.

The median line is meant to prevent accidental clashes between Chinese and Taiwanese forces. It is considered highly provocative for military planes to cross it.

Meanwhile, the Chinese military says it will launch important military exercises and training activities including live-fire drills in six areas surrounding Taiwan from Thursday.

The areas include Japan's exclusive economic zone. Taiwan media say they involve what Taiwan claims is its waters.

Pelosi's visit to Taiwan until Wednesday has drawn sharp reactions from China, which says Taiwan is integral part of its territory.