External pressure will not stop Taiwan engaging with the world, President Tsai Ing-wen said yesterday as she left for the United States, hitting a defiant note after China threatened retaliation if she met US House Speaker Kevin McCarthy.

China, which claims democratically-ruled Taiwan as its own territory, has repeatedly warned US officials not to meet Tsai, viewing it as support for the island's desire to be seen as a separate country.

The United States says such transits by Taiwanese presidents are routine and that China should not use Tsai's trip to take any aggressive moves against Taiwan.

The United States sees no reason for China to overreact to planned transits of the United States this week and next month by Taiwan's president, senior US officials said ahead of Tsai's departure.

China staged war games around Taiwan last August when then-US House Speaker Nancy Pelosi visited Taipei, and Taiwan's armed forces have said they are keeping watch for any Chinese moves when Tsai is abroad.

Tsai is going to Guatemala and Belize, transiting through New York first and Los Angeles on the way back. While not officially confirmed, she is expected to meet McCarthy while in California.

"External pressure will not hinder our determination to go to the world," she said at Taiwan's main international airport at Taoyuan, in a veiled reference to China.

"We are calm and confident, will neither yield nor provoke. Taiwan will firmly walk on the road of freedom and democracy and go into the world. Although this road is rough, Taiwan is not alone," added Tsai, who was due to arrive in New York yesterday afternoon.

Speaking in Beijing shortly before Tsai left, Zhu Fenglian, spokesperson of China's Taiwan Affairs Office, said Tsai's "transits" of the United States were not just her waiting at the airport or hotel, but for her to meet US officials and lawmakers.

"If she has contact with US House Speaker McCarthy, it will be another provocation that seriously violates the one-China principle, harms China's sovereignty and territorial integrity, and destroys peace and stability in the Taiwan Strait," she said.

"We firmly oppose this and will definitely take measures to resolutely fight back," Zhu added.