'We come in friendship to Taiwan, peace to the region': Pelosi

US House Speaker Nancy Pelosi said Wednesday that her delegation had come to Taiwan in "peace for the region", after the visit enraged Beijing and set off a diplomatic firestorm.

She landed in Taiwan late Tuesday, defying a string of increasingly stark warnings and threats from China, which views Taiwan as its territory and had warned it would consider her visit a major provocation.

Pelosi, second in line to the presidency, is the highest-profile elected US official to visit Taiwan in 25 years.

"We come in friendship to Taiwan, we come in peace to the region," she said during a meeting with Tsai Chi-chang, the deputy speaker of Taiwan's parliament.

As Pelosi -- who is on a tour of Asia -- touched down in a military aircraft after days of feverish speculation about her plans, the reaction from Beijing was swift.

US Ambassador Nicholas Burns was summoned by the Chinese foreign ministry late Tuesday and warned that Washington "shall pay the price".

"The move is extremely egregious in nature and the consequences are extremely serious," China's Vice Foreign Minister Xie Feng was quoted as saying by state news agency Xinhua.

"China will not sit idly by."

The Chinese military said it was on "high alert" and would "launch a series of targeted military actions in response" to the visit.

It promptly announced plans for a series of military exercises in waters around the island to begin on Wednesday, including "long-range live ammunition shooting" in the Taiwan Strait.

"Those who play with fire will perish by it," Beijing's foreign ministry added.

Taiwan's defence ministry said more than 21 Chinese military aircraft had flown on Tuesday into the island's air defence identification zone -- an area wider than its territorial airspace that overlaps with part of China's air defence zone.

China has vowed to seize self-ruled, democratic Taiwan one day, by force if necessary.

It tries to keep the island isolated on the world stage and opposes countries having official exchanges with Taipei.

In a call with US President Joe Biden last week, Chinese President Xi Jinping warned Washington against "playing with fire" on Taiwan.

While the Biden administration is understood to be opposed to Pelosi's Taiwan stop, White House National Security Council spokesman John Kirby said she was entitled to go where she pleased.

The United States has said, however, that its policy was unchanged towards Taiwan.

This means support for its government while diplomatically recognising Beijing over Taipei, and opposing a formal independence declaration by Taiwan or a forceful takeover by China.