Two Chinese ships have been spotted near islands at the centre of a heated dispute between Beijing and Tokyo, the Japan Coast Guard said on Saturday.
A Japanese patrol aircraft saw one Chinese fisheries patrol ship in waters near the disputed island chain in the East China sea around 8.25 am (2325 GMT), a coast guard spokeswoman said.
Around 20 minutes later, the Japan Coast Guard found another vessel in the area, she said, adding that Japan had dispatched patrol ships to tell the Chinese vessels to leave.
Japan and China both claim the potentially resource-rich islets, known as the Diaoyus in China and Senkakus in Japan, along with the nearby seas.
It was the first time since October 24 that Chinese patrol vessels had been seen operating in the region, Jiji Press said.
"The two vessels came as close as 23 km to the islands," she said, adding that the ships had not entered what Japan considers its waters.
"They seem to be travelling just outside our territorial waters," she said.
The Chinese sailors have told the Japan Coast Guard that they are there carrying out their duty, according to national broadcaster NHK.
The Japanese government has set up a team to relay up-to-date information on the potential incident to various ministries, Jiji Press said.
News of the encounter comes as Japan and China attempt to get their relationship back on an even keel.
A bitter row erupted in september when the Japan coast guard arrested a Chinese trawler captain for allegedly ramming two of its vessels in the area.
The arrest sparked serious protests by China, which cut or dramatically reduced political, cultural and economic exchanges with Japan.