The Liaoning and accompanying vessels entered Taiwan's air defence zone on Tuesday, the same day Chinese President Xi Jinping delivered a blistering nationalistic speech -- 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, which sees self-ruled Taiwan as its territory, has stepped up air and naval patrols around the island since Beijing-sceptic President Tsai Ing-wen came to power in May 2016.

She refuses publicly to accept the "one China" formula agreed between Beijing and Taiwan's previous government.

Chinese warplanes conducted 25 drills around Taiwan between August 2016 and mid-December last year, according to Taipei.

The Liaoning, currently China's only aircraft carrier, left around noon Wednesday, Taiwan's defence ministry said.

The 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 sailed past Taiwan again last July en route to Hong Kong and returned in January this year.

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.

The carrier's latest voyage came days after President Donald Trump signed new rules allowing top-level US officials to travel to Taiwan.

An irked Beijing has called on Washington to "correct its mistake".

US Deputy Assistant Secretary of State Alex Wong is currently visiting the island and will speak at a business dinner alongside President Tsai later Wednesday.

"We are monitoring the whole process of the Liaoning's cross-region drill," Defence Minister Yeh De-fa told parliament Wednesday.

The defence ministry said no unusual activities by the carrier group had been spotted "and we urge the public to rest assured".