Taiwan supporters hold signs during a rally in front of the Westin Bonaventure hotel where Taiwan President Tsai Ing-wen will spend the night ahead of meeting with Kevin McCarthy, in Los Angeles, April 4, 2023. ( AFP)
The meeting outside Los Angeles comes on what is technically a stopover for President Tsai Ing-wen, after her two-country trip in Latin America to visit Taiwan's few remaining official allies.
A pro-China demonstration also gathered nearby chanting "One China", as Tsai arrived Tuesday evening, following her Central American tour.
Beijing claims Taiwan as its own territory and balks at any official contact Taipei has with other countries.
This week, it warned McCarthy, a Republican and California native who is second in line to the US presidency, that he was "playing with fire" by meeting Tsai.
"China is strongly opposed to the US arranging for Tsai Ing-wen to transit through its territory, and is strongly opposed to the meeting between House Speaker Kevin McCarthy, the third-ranking US official, and Tsai Ing-wen," foreign ministry spokeswoman Mao Ning told reporters.
"It seriously violates the One-China principle and the three China-US joint communiques, and seriously undermines China's sovereignty and territorial integrity."
Taiwan, a flourishing democracy, has been self-governing for decades. It has its own military, an independent judiciary and all the trappings of a fully functioning state.
But only a handful of countries acknowledge it as a sovereign nation.
The United States formally recognizes Beijing, but is an important backer of Taiwan, and maintains strong unofficial ties.
Taipei enjoys strong bipartisan support in the US Congress, and has grown closer to Washington under Tsai's leadership.
Resolve to defend ourselves
Last year, McCarthy's predecessor, Democrat Nancy Pelosi sparked fury in Beijing by becoming the most senior US politician to visit the island in over two decades.
That prompted Beijing to launch its largest-ever military exercises in waters around Taiwan.
McCarthy had originally planned to go himself, but opted instead to meet Tsai at the Ronald Reagan Presidential Library in Simi Valley, California.
His office said that the meeting would be "bipartisan," while US media reported that over a dozen other members of Congress would attend.
The decision to meet in the United States was viewed as a compromise that would underscore support for Taiwan but avoid inflaming tensions with China.
Tsai's visit to southern California comes after trips to Guatemala and Belize and after a brief stop in New York last week, where she was greeted by flag-waving Taiwanese expatriates.
"We have demonstrated a firm will and resolve to defend ourselves, that we are capable of managing risks with calm and composure and that we have the ability to maintain regional peace and stability," she said in New York.
Bonnie Glaser, Managing Director of the Indo-Pacific Program at the German Marshall Fund, said China had been quite outspoken about the visit in recent days, and may feel that it has to keep up the rhetoric.
"China has already said some fairly threatening things which suggests to me that they have to respond in some way," she told AFP, adding that "otherwise (President) Xi Jinping could end up looking weak."
But China's response will be shaped in part, Glaser said, by what McCarthy says publicly after the meeting.
China's consulate in Los Angeles said on Monday the meeting in California would "greatly hurt the national feelings of 1.4 billion Chinese people" and undermine "the political foundation of China-US relations."