Japan's Coast Guard has detected two Chinese vessels entering Japanese territorial waters near the disputed Senkaku/Diaoyu Islands, NHK reported Sunday.
According to the report, the two vessels attempted to approach Japanese fishing boats.
Japan's Coast Guard Headquarters then deployed patrol boats to the area and warned the Chinese vessels to leave what Japan considered its territorial waters immediately.
According to NHK, this was the 18th time that a China Coast Guard vessel has crossed into the disputed waters off the coast of the Senkaku Islands since 28 August.
The islands in question have long been an object of territorial disputes between China and Japan. Tokyo maintains it has had sovereignty over them since 1895 and Beijing claims that the islands are marked as a Chinese territory on Japanese maps circa 1783 and 1785.
Following World War II, the islands were controlled by the United States and handed over to Japan in 1972. China believes Japan illegally seized them, while Tokyo maintains that Beijing began claiming the islands after the 1970s, when the surrounding water area was found to be full of valuable minerals.
The tensions were exacerbated after the Japanese government bought three of the islands from a private owner in 2012.