Japan protests to China over ship in disputed waters

Japan administers the uninhabited Senkaku islands, which China also claims under the name Diaoyu islands.

In 2012, relations between Japan and China deteriorated after Japan bought the islands from a private owner.

The islands are important because they are close to key shipping lanes, offer rich fishing grounds and lie near potential oil and gas reserves.

At a news conference Japan's chief cabinet secretary Yoshihide Suga reacted to the incident, expressing "serious concern that it would escalate tensions.”

“Prime minister Shinzo Abe has told his government to work closely with the US and other countries to deal with this,” Suga said.

"Around 16:30 CET on Wednesday, a Chinese naval vessel entered our nation's contiguous waters surrounding the Senkaku Islands," the Japanese foreign ministry said in a statement.

Japan's vice-foreign minister Akitaka Saiki summoned China's ambassador Cheng Yonghua to lodge a protest.

Saiki told the ambassador that the Senkakus are an inherent part of Japan's territory, in terms of history and international law, NHK reported.

“I demand that the vessel swiftly move away from the area,”he said.

Local media reported the vessel left the area around 20:10 CET.

According to Kyodo news agency, Cheng said the Chinese frigate was allowed to sail in those waters.