China, which claims Taiwan as its own territory, opposes any foreign interactions or visits by the island's leaders, especially those involving the United States.

A spokesperson for the U.S. State Department reiterated the U.S. position that transits by high-level Taiwan authorities were routine and "consistent with long-standing practice, the unofficial nature of our relations with Taiwan, and the U.S. One-China policy, which remains unchanged."

"We see no justification for a private, routine, and unofficial transit to be used as a pretext for provocation," the spokesperson added.

China is likely to launch military drills in the coming days near Taiwan, using Lai's trip to the Pacific and scheduled stopovers in the United States as a pretext, according to assessments by Taiwan and regional security officials.

Lai's weeklong trip begins on Saturday, making what is officially called a stopover first in Hawaii before going to the Marshall Islands, Tuvalu and Palau, three of the 12 countries which have formal ties with Taiwan.

He will also stop over in the U.S. territory of Guam.

Mao Ning, a spokesperson for China's foreign ministry, reiterated comments made by President Xi Jinping to U.S. President Joe Biden at an Asia-Pacific summit in Peru this month, in which he said "separatist acts" were incompatible with peace and stability in the Taiwan Strait.

"If the United States wants to maintain peace in the Taiwan Straits, it is crucial for it to recognise the independence nature of Lai Ching-te and the Democratic Progressive Party authorities," she said, referring to Taiwan's ruling party.

The United States must "handle the Taiwan issue with utmost caution, unequivocally oppose Taiwan independence, and support the peaceful reunification of China", Mao added at a daily news briefing in the Chinese capital.

China opposes any "scurrying to the United States" of Taiwan's leaders, in any form, or any U.S. support for separatist activities, she said.

"China's determination to defend its national sovereignty and territorial integrity and oppose interference in its internal affairs by external forces is unwavering."

The State Department spokesperson said every democratically elected Taiwan president had transited the United States, with Taiwan's former President Tsai Ing-wen making seven overseas trips with U.S. transits, while her predecessor Ma Ying-jeou transited several times as well, with both going via Hawaii twice.

The official said that as with past transits, Lai would be welcomed in Hawaii by Ingrid Larson, Washington office managing director of the American Institute in Taiwan, the body which serves as the unofficial U.S. embassy in Taiwan.

Taiwan Foreign Minister Lin Chia-lung told lawmakers on Thursday that Chinese war games in response to Lai's trip were one of the possible scenarios.

Lai and his government reject Beijing's sovereignty claims, saying only the island's people can decide their future.

Visiting a temple in New Taipei on Friday, Lai said he was looking forward to visiting Taiwan's three Pacific allies on his first overseas visit since assuming office in May.

Lai said he would keep deepening partnership with other countries and "keep Taiwan going out into the world", the presidential office said in a statement that did not mention the U.S. stopovers.