Seven Chinese ships sailed into waters around islands at the center of a bitter dispute with Japan on Tuesday, the day before the anniversary of Tokyo's nationalisation of part of the chain.

The Chinese coast guard flotilla is the biggest seen in waters around the Tokyo-administered Senkakus since eight government ships were tracked there in April, a spokesman for the Japanese coast guard said.

Official media in China, citing the State Oceanic Administration (SOA), said it was the 59th "patrol" of the area since September 2012, when Tokyo took the islands into public ownership.

Beijing claims the archipelago as its own and calls the islands the Diaoyus.

Japan's coast guard said the vessels had entered Japanese territorial waters around 10:30 a.m.

The incident came almost a year to the day since the long-running dispute over the ownership of the islands flared into a bitter row that continues to dog relations.

The islands -- believed to harbor vast natural resources below their seabed -- are seen as a potential flashpoint that some observers fear could lead to armed conflict between the Asian giants.

On Monday, Japan scrambled fighter jets after an unidentified drone flew near the islands. The drone did not enter Japanese airspace.

On Sunday, Japan tracked Chinese bombers that flew in international airspace between two islands in the Okinawa chain. Tokyo said was the first time they had used that route to get to the Pacific.

© (C) 2013 AFP