Los Angeles, California - Taiwan President Tsai Ing-wen on Wednesday met with US House Speaker Kevin McCarthy during a stopover in California, a high-profile visit denounced by China as a provocation.

Tsai, who attended a bipartisan meeting held by McCarthy at the Ronald Reagan Presidential Library outside of Los Angeles, warned that "democracy is under threat" as she spoke alongside the US speaker in his home state.

"It is no secret that today the peace we have maintained and the democracy which we have worked hard to build are facing unprecedented challenges," Tsai said.

"We once again find ourselves in a world where democracy is under threat and the urgency of keeping the beacon of freedom shining cannot be understated."

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Speaking to the press, McCarthy said he had a "very productive discussion" with the Taiwanese leader.

"Based on our conversation, it's clear several actions are necessary: first, we must continue arms sales to Taiwan and make sure such sales reach Taiwan on a very timely basis," the top House Republican said, while also stressing the need for more economic cooperation.

Tsai stopped in the US on her return from Central America, where she met with the leaders of Guatemala and Belize. The White House insists her time in the US is not an official visit.

Beijing regards Taiwan as part of China and it rejects any official contact between countries and Taipei.

The Foreign Ministry in Beijing "firmly" condemned and opposed the visit, which it called "a serious violation of the one-China principle."

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"It seriously infringes upon China's sovereignty and territorial integrity and sends an egregiously wrong signal to the 'Taiwan independence' separatist forces," the ministry said in a statement. "China firmly opposes and strongly condemns it."

The ministry went on to say that Washington "has been crossing the line and acting provocatively on issues such as US-Taiwan official exchanges, arms sales to and military dealings with Taiwan."

Beijing warned Washington to "not go further down the wrong and dangerous path."

China has previously raised the prospect of taking the island by force if necessary, with the US threatening to take action if that happens. Taiwan is a self-governing democracy and has long seen itself as independent.

Asked about the visit in Brussels earlier on Wednesday, US Secretary of State Antony Blinken warned Beijing not to use Tsai's stopover "as an excuse to take any actions to ratchet up tensions."