Japan on Monday lodged a protest with the Chinese government, saying two Chinese ships which entered Japanese waters surrounding a group of disputed islands in the East China Sea had to withdraw immediately, reported dpa.
The maritime survey ships entered the waters around the islands, which are known as Senkaku in Japan and Diaoyu in China, earlier Monday, the Kyodo News agency said.
"Such activity is extremely regrettable and we demand immediate withdrawal," Chief Cabinet Secretary Takeo Kawamura said. "The Ministry of Foreign Affairs quickly lodged a protest with the Chinese government."
Japan has held the islands, which have caused bilateral tension several times in the past, since China's defeat in the Sino-Japanese War in 1895, but they are also claimed by China and Taiwan.
The latest incident is the first of its kind since 2004. However, it is not likely to scuttle a trilateral summit between the leaders of Japan, China and South Korea scheduled for December 13, Kawamura said.