More than 20 Chinese military planes flew into Taiwan's air defence zone on Tuesday, officials in Taipei said, as US House Speaker Nancy Pelosi began her controversial visit to the self-ruled island that Beijing considers its territory.

The island's defence ministry said in a statement on Twitter: "21 PLA aircraft ... entered #Taiwan's southwest ADIZ on August 2, 2022," referring to the air defence identification zone.

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.