Chinese spy ship entered Japan waters: Tokyo

A Chinese spy ship entered Japan's territorial waters today, Tokyo officials said, less than a week after another of the rival's naval vessels sailed near islands at the centre of a sovereignty dispute.

Concerns over China's rising military presence in Asian waters have sparked concerns in Japan, which administers islands in the East China Sea also claimed by Beijing and where tensions between the two powers have festered.

A Japanese navy P-3C surveillance aircraft spotted the 6,096-ton Dongdiao-class "information gathering" Chinese vessel around 3:30 am (local time) in territorial waters near Kuchinoerabu island in southern Japan, Hiroshige Seko, a government spokesman, told reporters.

Territorial waters are a 12-nautical-mile band, though Japan did not immediately say by how much the Chinese ship breached them.

The area is part of a Japanese island chain that divides the East China Sea and the Pacific Ocean, and is not subject to the territorial dispute.

The Chinese ship sailed southeast and exited Japanese waters around 5 am heading into the Pacific, Seko told a regular press briefing.

Today's reported incursion came less than a week after another Chinese naval ship sailed close to the disputed islands, though did not enter what Japan sees as territorial waters.

Japan said last week that a Jiangkai class Chinese frigate sailed into "contiguous waters" surrounding the contested East China Sea islands last Thursday.

Contiguous waters are a 12-nautical-mile band that extends beyond territorial waters. Under international rules, they are not the preserve of any single country, although the resident power has certain limited rights.

It marked the first time a Chinese navy ship had approached so close to the disputed islets and an angry Japan summoned Beijing's ambassador to protest.

China does not recognise Japan's claim to the islands -- known as Senkaku in Japan and Diaoyu in China -- and says its ships have the right to sail freely in Chinese territorial waters.

International laws allow ships of all states to exercise the right of "innocent passage" through the territorial sea. A Chinese nuclear submarine entered Japanese waters in 2004.

Relations between Japan and China deteriorated in 2012 when Tokyo "nationalised" some of the disputed uninhabited islets. The countries have taken steps to mend fences but relations remain tense.

The response from Japan this time was more muted, however, with the government conveying its "concerns about the Chinese military's activities in general", Seko said.

"The government will continue to take thorough measures to patrol the air space and waters surrounding our nation," he added.

Japan has expressed concern over Chinese land reclamation and expansion of military facilities in the South China Sea, where Beijing has disputes with countries including Vietnam and the Philippines.