'Taiwan question is our red line,' China tells Japan

China strongly criticized a visit by Japanese lawmakers to Taiwan, telling Tokyo that Taiwan is a red line for Beijing that cannot be crossed, state-run media said on Thursday.

Chinese Foreign Ministry spokesperson Lin Jian said that there is only one China and Taiwan is an inseparable part of China's territory, CGTN reported.

"We firmly oppose any form of official interaction between the Taiwan region and countries having diplomatic ties with China and have lodged serious protests with the Japanese side," Lin said.

His reaction came after reports that a member of Japan's House of Representatives-a former secretary-general of the ruling Liberal Democratic Party (LDP)-along with other Japanese parliamentarians visited the self-governed island and met with its leader Lai Ching-te and others.

"Japan committed innumerable crimes during its 50 years of colonial rule over Taiwan, and is responsible for the enormous sins witnessed by history against the Chinese people," said Lin, urging Japan to adhere to the one-China principle and the spirit of the four political documents between the two countries.

Separately, the China Coast Guard on Thursday said they had expelled a Japanese vessel that "trespassed" in Chinese territorial waters off the Diaoyu Islands.

In a short statement, the coast guard urged Tokyo to immediately cease all "illegal" activities in these waters.

"CCG vessels will continue to conduct maritime rights protection and law enforcement activities in our jurisdictional waters to safeguard national sovereignty, security, and maritime rights," the state-run Global Times reported.