The speaker of the US House of Representatives landed in Taipei at 10.45pm local time (3.45pm BST), becoming the highest-profile American official to visit in 25 years.
The 82-year-old said ahead of the visit that her trip, which was only confirmed at the last minute in the face of fierce opposition from Beijing, showed “America’s solidarity with the 23 million people of Taiwan... as the world faces a choice between autocracy and democracy”.
China condemned the visit as a threat to peace and stability in the Taiwan Strait, responding by summoning the US ambassador in Beijing and announcing the suspension of several agricultural imports from Taiwan.
Beijing called the visit “extremely dangerous” and announced it would conduct live-fire exercises in the waters around the island.
According to a map published by state media, China could fire missiles into target zones that would breach Taiwan’s internal waters. Beijing has not fired so close to the self-governing island since 1996.
Xi Jinping, China’s president, has vowed to reunite Taiwan with the mainland. The US operates a policy of strategic ambiguity on Taiwan, recognising China’s claim to the territory while being bound by law to provide the island with the means to defend itself against aggression.
Taipei said that more than 20 Chinese aircraft had entered its air defence zone, less of an escalation than breaching its airspace, while Chinese warships were stationed to the east. Video published by Chinese state media showed amphibious tanks lining up on the beach opposite Taiwan on the mainland.
Taiwan’s defence ministry said that the drills were meant to “psychologically intimidate” citizens and announced it had “reinforced” the alert level of its military.
Ms Pelosi, a long-time critic of China, was under heightened security at the Grand Hyatt Hotel in Taipei.
In an opinion piece for The Washington Post published after her arrival in Taipei, Ms Pelosi wrote that her visit was a symbol to the “millions... oppressed and menaced by the PRC [People’s Republic of China]”, referencing the crackdown on Hong Kong and Uyghur Muslims.
Joe Biden, the US president, had warned against the escalatory visit but does not dictate his lawmakers’ travel decisions.
Antony Blinken, the US secretary of state, said that the trip would be entirely Ms Pelosi’s decision, and called on Beijing to “act responsibly and not to engage in any escalation going forward”.
Four US warships, including the aircraft carrier USS Ronald Reagan, were positioned in waters east of Taiwan on what the US Navy called routine deployments.
Taipei’s foreign ministry said that the trip showed Washington’s “rock solid” support, amid backing in Washington from both Democratic hawks and large parts of the China-wary Republican party.
Bonnie Glaser, the director of the Asia programme at the US-based German Marshall Fund think tank, said that the probability of Beijing choosing war was “low”.
“But the probability that... [China] will take a series of military, economic, and diplomatic actions to show strength & resolve is not insignificant,” she said.
“The Chinese feel if they don’t act, the US is going to continue to slice the salami… They are trying to draw that red line brighter and thicker.”
Ahead of Ms Pelosi’s arrival, the Chinese military began live-fire drills in the South China Sea, while military exercises were also being carried out in the northern Bohai Sea.
Two Chinese warships – a destroyer and a guided missile frigate – were stationed in waters east of Taiwan, according to Japan’s defence ministry.
Videos circulated on Chinese social media purportedly showing Chinese amphibious tanks on a beach in the city of Xiamen, along the Taiwan Strait.
In addition, several Chinese warplanes flew close to the median line dividing the Taiwan Strait on Tuesday morning, according to Reuters.
The visit is an unofficial stop on Ms Pelosi’s Asian tour, which also includes stops in Singapore on Monday and Malaysia on Tuesday, with South Korea and Japan also on the itinerary.
In the lead-up to her expected arrival, Taiwan’s most iconic building, Taipei 101, lit up with messages:
— Yimou Lee (@YimouLee) August 2, 2022
Before Ms Pelosi’s arrival, the Chinese foreign ministry said that the US will “pay the price” if she visited Taiwan.
“The US side will bear the responsibility... for undermining China’s sovereign security interests,” Hua Chunying, the foreign ministry spokesman said.
China considers self-ruled Taiwan a breakaway province that may be reconquered by force if necessary and bristles at other countries’ top-level exchanges with the island’s government.
Earlier on Tuesday, China’s Xiamen Airlines announced it was cancelling flights due to “limitations in the air space” near the Taiwan Strait.
The People’s Liberation Army said late on Monday that its forces were on “high alert” and would “engage the enemy on orders.” The statement said the forces would “bury all invaders” and “march toward victory”.
Taiwan’s defence ministry said on Tuesday it had a full grasp of military activities near Taiwan and would send forces in reaction to “enemy threats”.
“We are meticulously preparing various plans and appropriate troops will be dispatched to respond in accordance with the regulations of emergency situation responses and the threat posed by the enemy,” the ministry said.
On Tuesday night, China's UK ambassador Zheng Zeguang vowed "severe consequences" if British politicians visit Taiwan, the Guardian reported.
Visits would interfere in China's internal affairs and would lead to severe consequences in China-UK relations, Mr Zheng said at a news conference in London.
"We call on the UK side to abide by the Sino-UK joint communique and not to underestimate the extreme sensitivity of the Taiwan issue, and not to follow the US's footsteps," Mr Zheng said.