United States House Speaker Nancy Pelosi landed in Taiwan on Tuesday evening, defying a string of increasingly stark warnings and threats from China that have sent tensions between the world's two superpowers soaring.
China immediately condemned Pelosi's visit, with the Foreign Ministry saying it seriously damages peace and stability in the Taiwan Strait "has a severe impact on the political foundation of China-US relations, and seriously infringes upon China's sovereignty and territorial integrity."
The ministry said it had lodged a strong protest with the US.
Meanwhile, the Chinese military has been put on high alert and will launch "targeted military operations" in response to the visit to Taiwan.
Separately, the People's Liberation Army was supposed to conduct joint military operations near Taiwan from Tuesday night, and test-launch conventional missiles in the sea east of Taiwan.
As Pelosi's plane neared Taipei Chinese state media said advanced Su-35 fighter jets were crossing the Taiwan Strait.
Pelosi, second in line to the presidency, is the highest-profile elected US official to visit Taiwan in 25 years and Beijing has made clear that it regards her presence as a major provocation, setting the region on edge.
Live broadcasts showed the 82-year-old lawmaker, who flew on a US military aircraft, being greeted at Taipei's Songshan Airport by Foreign Minister Joseph Wu.
"Our delegation's visit to Taiwan honors America's unwavering commitment to supporting Taiwan's vibrant democracy," Pelosi's official Twitter account wrote.
"America's solidarity with the 23 million people of Taiwan is more important today than ever, as the world faces a choice between autocracy and democracy."
She added her visit "in no way contradicts" US policy towards Taiwan and Beijing.
Pelosi is currently on a tour of Asia and while neither she nor her office confirmed the Taipei visit, multiple US and Taiwanese media outlets reported it was on the cards -- triggering days of building anger from Beijing.
In a Washington Post opinion piece released shortly after she landed, Pelosi outlined her reasons for visiting, praising Taiwan's commitment to democratic government while criticizing China as having dramatically increased tensions with Taiwan in recent years.
She also cited China's "brutal crackdown" against political dissent in Hong Kong, as well as its treatment of Muslim Uighurs and other minorities.
Chinese Foreign Minister Wang Yi said earlier on Tuesday that US politicians who "play with fire" on the Taiwan issue will "come to no good end".
White House national security spokesperson John Kirby said the visit is not a violation of either any sovereignty issues or America's longstanding "one-China policy."
"There's no reason for this visit to become a spurring event for a crisis or conflict," Kirby added.
Taiwan's President Tsai Ing-wen will meet with Pelosi on Wednesday morning and would have lunch with her. Four sources said she was also scheduled in the afternoon to meet a group of activists who are outspoken about China's human rights record.
China considers self-ruled, democratic Taiwan as its territory and has vowed to one day seize the island, by force if necessary.
It tries to keep Taiwan isolated on the world stage and opposes countries having official exchanges with Taipei.
China last week warned US against "playing with fire" on Taiwan.
Moscow said it was "absolutely in solidarity with China", calling the prospect of a Pelosi visit "pure provocation".