Japan on Tuesday accused China of sending ships into its territorial waters around disputed Senkaku Islands.
Officials from Japan Coast Guard said: "two Chinese government ships have entered Japan's territorial waters near the Senkaku Islands in the East China Sea."
"The ships entered waters off Uotsuri Island at around 4.10 a.m. on Tuesday (1910GMT Monday). The ships apparently tried to approach a Japanese fishing boat operating in the area," the officials told Japanese public broadcaster NHK.
The Japanese Coast Guard patrols urged the Chinese vessels to "immediately leave Japan's territorial waters."
Beijing and Tokyo are locked in a dispute over the Japanese-controlled Senkaku Islands, which Beijing claims and calls Diaoyu.
Tokyo said it was 11th time this year that "Chinese government ships have been spotted entering Japanese territorial waters off the islands."
The last alleged intrusion was reported on June 18.
On Monday, Japan's Foreign Ministry claimed China had "set up a new drilling facility for gas fields in a contested area of the East China Sea."
Tokyo has lodged protest with the Chinese Embassy and urged Beijing to halt "its unilateral resource development program there."
"The facility is located on the Chinese side of a Tokyo-proposed median line separating the countries' exclusive economic zones in the sea," the ministry said.
The two countries agreed in 2008 on joint gas development in the area but "negotiations were suspended in 2010 when tensions between them increased following a Chinese trawler's collision with a Japan Coast Guard vessel," according to Kyodo News.
