Taiwan's President Tsai Ing-wen arrived in New York Wednesday for a visit that has triggered threats of reprisal by China if she meets with House speaker Kevin McCarthy -- and US warnings for Beijing not to overreact.

Tsai is stopping over in the United States en route to Central America, where she will meet with the leaders of Guatemala and Belize to shore up ties with those diplomatic allies. On her way back to Taiwan she will stop in California, where McCarthy had said he would meet her.

China claims the democratic island as part of its territory to be retaken one day and, under its "One China" principle, no country may maintain official ties with both Beijing and Taipei.

Beijing warned Wednesday that it was "resolutely opposed" to any meeting between Tsai and McCarthy and vowed to take "resolute measures to fight back" if it goes ahead.

"If (Tsai) engages with US House Speaker McCarthy, it will be another provocation that seriously violates the One China principle, undermines China's sovereignty and territorial integrity, and undermines peace and stability across the Taiwan Strait," Taiwan Affairs Office spokesperson Zhu Fenglian said.

The United States responded by saying China should not use Tsai's stopover "as a pretext to step up any aggressive activity around the Taiwan Strait."

"There's no reason for them to react harshly," White House National Security spokesman John Kirby told reporters.

"This transit is consistent with our longstanding unofficial relationship with Taiwan and it is consistent with the United States One China policy, which remains unchanged," Kirby said.

Outside her hotel in New York, dozens of pro-Beijing demonstrators waving China's red flag gathered boisterously while nearby a similarly sized group of pro-Taiwan people cheered and waved their banner and the US stars and stripes.

Tsai's trip follows Honduras's decision this month to open diplomatic relations with Beijing, leaving Belize and Guatemala among just 13 countries that have official ties with Taipei.

"External pressure will not hinder our determination to go global," Tsai told reporters at the airport before leaving. "We are calm and confident. We will not succumb and we will not provoke (others)."