Relations have been strained since Japan's new Prime Minister Sanae Takaichi suggested last month that her country could intervene militarily in any Chinese attack on Taiwan.

Japan's coast guard said two Chinese coast guard patrol ships entered Japan's territorial waters around the Senkaku Islands in the East China Sea in the early hours of Tuesday, and left a few hours later.

The Japanese-administered Senkaku Islands, known as the Diaoyu in China, have been a regular flashpoint between the two nations over the decades.

After the patrol ships sailed toward a Japanese fishing boat, a Japanese coast guard vessel issued a demand that they leave the waters, the Japanese coast guard statement said.

"The activities of Chinese coast guard vessels navigating within Japan's territorial waters around the Senkaku Islands while asserting their own claims fundamentally violate international law," it said.

The statement added that the two Chinese vessels, and others, were still in the area.

China Coast Guard spokesman Liu Dejun said that a Japanese fishing vessel "illegally entered China's territorial waters".

"China Coast Guard vessels took necessary control measures and made warnings to drive it away," Liu said on the China Coast Guard's official WeChat account.

"The China Coast Guard will continue to conduct rights protection and law enforcement activities in the waters around the Diaoyu Islands, resolutely safeguarding national territorial sovereignty and maritime rights," he added.

It followed a similar incident around the islands on November 16, around a week after Takaichi's comments, Kyodo News reported.

China claims self-ruled Taiwan as part of its territory and has not ruled out using force to take the democratic island.

Beijing has urged its citizens to avoid travel to Japan and a number of cultural events have been hit -- including the halt of a performance by a Japanese singer in Shanghai on Friday.

Aside from reportedly renewing a ban on Japanese seafood imports, China has however so far stopped short of imposing more serious economic measures such as curbing exports of rare earth metals.