The Liaoning and accompanying vessels entered Taiwan's air defence zone on Tuesday and left around noon Wednesday, the ministry said.

Chinese President Xi Jinping delivered a blistering nationalist speech on Tuesday, warning against what he called any attempts to split China.

"All acts and tricks to separate the country are doomed to fail and will be condemned by the people and punished by history," Xi said in an address ending the annual session of the National People's Congress.

China still sees Taiwan as its territory awaiting reunification, by force if necessary, even though the two sides split in 1949 after a civil war and have been ruled separately ever since.

Ties have turned frosty since Taiwan's Beijing-sceptic President Tsai Ing-wen came to power. Her government refuses to acknowledge that the island is part of "one China".

Tsai has warned against what she called China's military expansion -- the increase in air and naval drills around the island since she took office in May 2016.

The aircraft carrier -- a second-hand Soviet-built ship -- caused a stir in Taiwan when it first entered the strait in January last year in what was seen as a show of strength by Beijing.

It returned in January this year.

"We are monitoring the whole process of the Liaoning's cross-region drill," Defence Minister Yeh De-fa told parliament Wednesday when asked to comment on its latest moves.

The defence ministry said in a statement that it sent aircraft and vessels to conduct surveillance. "No unusual activities have been spotted and we urge the public to rest assured," it said.