US House Speaker Nancy Pelosi has left Taiwan after a visit that heightened tensions with China, saying that she and other members of Congress in her delegation showed they will not abandon their commitment to the self-governing island.

Ms Pelosi, the first US speaker to visit the island in more than 25 years, courted Beijing’s wrath with the visit and set off more than a week of debate over whether it was a good idea after news of it leaked.

In Taipei she remained calm but defiant.

“Today the world faces a choice between democracy and autocracy,” she said in a short speech during a meeting with Taiwanese President Tsai Ing-wen.

“America’s determination to preserve democracy, here in Taiwan and around the world, remains ironclad.”

China, which claims Taiwan as its territory and opposes any engagement by Taiwanese officials with foreign governments, announced multiple military exercises around the island, parts of which will enter Taiwanese waters, and issued a series of harsh statements after the delegation touched down on Tuesday night in the Taiwanese capital Taipei.

Taiwan decried the planned actions, saying they violated the island’s sovereignty.

“Such an act equals to sealing off Taiwan by air and sea, such an act covers our country’s territory and territorial waters, and severely violates our country’s territorial sovereignty,” Captain Jian-chang Yu said at a briefing by the National Defence Ministry.

The Chinese military exercises, including live fire, are to start on Thursday and be the largest aimed at Taiwan since 1995, when China fired missiles in a large-scale exercise to show its displeasure at a visit by then-Taiwanese president Lee Teng-hui to the US.

Taiwanese President Ms Tsai responded firmly on Wednesday to Beijing’s military intimidation.

“Facing deliberately heightened military threats, Taiwan will not back down,” Ms Tsai said at her meeting with Ms Pelosi.

“We will firmly uphold our nation’s sovereignty and continue to hold the line of defence for democracy.”

China’s official Xinhua News Agency announced the military actions on Tuesday night, along with a map outlining six different areas around Taiwan.

Arthur Zhin-Sheng Wang, a defence studies expert at Taiwan’s Central Police University, said three of the areas infringe on Taiwanese waters, meaning they are within 12 nautical miles of shore.

Using live fire in a country’s territorial airspace or waters is risky, said Mr Wang, adding that “according to international rules of engagement, this can possibly be seen as an act of war”.

Ms Pelosi’s trip has heightened US-China tensions more than visits by other members of Congress because of her high-level position as leader of the House of Representatives.

She is the first speaker of the House to visit Taiwan in 25 years, since Newt Gingrich in 1997.

However, other members of Congress have visited Taiwan in the past year.

Ms Tsai, thanking Ms Pelosi for her decades of support for Taiwan, presented the speaker with a civilian honour, the Order of the Propitious Clouds.

China’s response has been loud and has come on multiple fronts: diplomatic, economic and military.

Shortly after Ms Pelosi landed on Tuesday night, China announced live-fire drills that reportedly started that night, as well as the four-day exercises starting on Thursday.

The People’s Liberation Army Air Force also flew a contingent of 21 war planes on Tuesday night, including fighter jets, towards Taiwan.

Chinese vice foreign minister Xie Feng summoned the US ambassador in Beijing, Nicholas Burns, to convey the country’s protests the same night.

On Wednesday, China also banned some imports from Taiwan, including citrus fruit and fish.

Chinese state broadcaster CCTV published images of PLA drills and video on Wednesday, although it was unclear where they were being conducted.

Ms Pelosi addressed Beijing’s threats on Wednesday morning, saying she hopes it is clear that while China has prevented Taiwan from attending certain international meetings, “that they understand they will not stand in the way of people coming to Taiwan as a show of friendship and of support”.

She noted that support for Taiwan is bipartisan in Congress and praised the island’s democracy.

She stopped short of saying that the US would defend Taiwan militarily, emphasising that Congress is “committed to the security of Taiwan, in order to have Taiwan be able to most effectively defend themselves”.

Her focus has always been the same, she said, going back to her 1991 visit to Beijing’s Tiananmen Square, when she and other legislators unfurled a small banner supporting democracy two years after a bloody military crackdown on protesters at the square.

That visit was also about human rights and what she called dangerous technology transfers to “rogue countries”.

Ms Pelosi visited a human rights museum in Taipei that details the history of the island’s martial law era and met with some of Taiwan’s most prominent rights activists, including an exiled former Hong Kong bookseller who was detained by Chinese authorities, Lam Wing-kee.

Ms Pelosi, who is leading the trip with five other members of Congress, also met with representatives from Taiwan’s legislature.

“Madam Speaker’s visit to Taiwan with the delegation, without fear, is the strongest defence of upholding human rights and consolidation of the values of democracy and freedom,” Tsai Chi-chang, vice president of Taiwan’s legislature, said in welcome.

The administration of US President Joe Biden has sought to tone down the volume on the visit, insisting there is no change in America’s longstanding “one-China policy”, which recognises Beijing but allows informal relations and defence ties with Taipei.

Ms Pelosi said her delegation has “heft”, including Gregory Meeks, chairman of the House Foreign Affairs Committee, and Raja Krishnamoorthi, from the House Intelligence Committee.

Representatives Andy Kim and Mark Takano are also in the delegation.

She also mentioned Representative Suzan DelBene, whom Ms Pelosi said was instrumental in the passage of a 280 billion dollar Bill aimed at boosting American manufacturing and research in semiconductor chips – an industry that Taiwan dominates and is vital for modern electronics.

Ms Pelosi departed on Wednesday evening for South Korea, the next stop on an Asia tour that also included Singapore, Malaysia and Japan.