China has lodged serious protests with the Philippines after Philippine President Ferdinand Marcos Jr said his country could not "stay out" of a potential confrontation over the Taiwan region between China and the United States.

Speaking to Indian news website Firstpost on Wednesday during his official visit to the South Asian country, Marcos said that in the event of an "all-out war" across the Taiwan Strait, the Philippines would "be joined into it", citing the country's geographic proximity to Taiwan and the presence of many Filipinos there.

"How to settle the Taiwan question is a matter for the Chinese ourselves, which brooks no interference," a Chinese Foreign Ministry spokesperson said on Friday. The spokesperson stressed that there is only one China in the world, Taiwan is an inalienable part of China's territory, and the Taiwan question is an internal affair at the very core of China's core interests.

Manila, the spokesperson noted, has previously made serious commitments to China that it adheres to the one-China policy, recognizing Taiwan as part of China, and acknowledging that the matter should be resolved by the Chinese people.

"These words are written in black and white, but the Philippines is now going back on its words in disregard of the grave consequences," the spokesperson said.

Rejecting Manila's reasoning, the spokesperson said that using "geographic location" and the "large volume of Filipinos" as pretexts to interfere in the internal and sovereign affairs of other countries not only violates international law and the ASEAN Charter, but also harms regional peace and stability and the fundamental interests of the Philippine people.

"We urge the Philippines to earnestly abide by the one-China principle and the spirit of the China-Philippines Joint Communique on the establishment of diplomatic relations, and refrain from playing fire on issues bearing on China's core interests," the spokesperson added.

In a separate development, Jiang Bin, spokesman for the Ministry of National Defense, voiced on Friday strong opposition to any form of official contact or military connection between the US and the Taiwan region, amid reports that the chairman of the US Senate Committee on Armed Services may soon lead a congressional delegation to Taiwan — the first such visit by a senator in that position since 2016.

Jiang urged Washington to abide by the one-China principle and stipulations of the three China-US joint communiques, earnestly fulfill its promise of not supporting "Taiwan independence" and stop conniving at or supporting "Taiwan independence" separatist forces.

"The People's Liberation Army will stay on high alert and take resolute measures to safeguard national sovereignty and territorial integrity," Jiang said.