A Chinese submarine rescue ship sails in waters off the island of Yonaguni in Japan's Okinawa prefecture (AP/Japan Joint Staff Office)
Japan and China are trading a new round of criticism after Japanese military aircraft spotted seven Chinese warships in waters off a southern island not far from a chain of isles at the centre of a heated territory dispute.
China said the ships were on a routine training mission.
The Chinese ships were sighted about 30 miles from the island of Yonaguni, in Japan's Okinawa prefecture, according to Japan's Defence Ministry. They were about 125 miles from a chain of small islands that have sparked a heated dispute between Japan and China.
The ships were believed to be returning to China after training in the Pacific.
Japan's Defence Ministry said the ships were not headed for the disputed islands, but said it was the first time the Chinese navy has been spotted using the narrow sea passage near Yonaguni.
Defence Minister Satoshi Morimoto said Japan is monitoring the ships' movement. Japan considers the area part of its contiguous waters, but it is not illegal for foreign vessels to transit them.
It is not unusual for the Chinese navy to transit waters around Okinawa en route to the Pacific, but they usually go through wider straits. The ships included frigates, a guided missile destroyer, a supply ship and two submarine rescue vessels.
Defence Ministry officials said the ships might have been trying to avoid an approaching typhoon. China's Defence Ministry said the ships were on a scheduled cruising exercise and were acting in a manner that was "appropriate and legal".
Underscoring China's sharper stance, it also protested the scrambling of a Japanese military plane in the direction of the disputed islands, calling that a "gross violation" of Chinese sovereign rights. The ministry said in a short statement on its website: "The Chinese military is closely following the actions of the Japanese side and demands Japan halt all actions complicating or escalating the situation."
Japan angered China last month by nationalising part of the chain of uninhabited East China Sea islands called Senkaku in Japanese and Diaoyu in Chinese. The move sparked violent protests in China.