Two Chinese fishery patrol boats were spotted today off islands at the centre of a bitter dispute between Beijing and Tokyo, Japan's coastguard said.
The two vessels began cruising in waters close to the islands, known as Senkaku in Japan and Diaoyu in China, at around 7:40 am (local time), a coastguard official said.
"They are still navigating off the Senkaku islands, and our patrol ships and air planes are warning them by radio not to enter Japanese territorial waters," she said.
Both Tokyo and Beijing claim the potentially resource-rich islands, along with their surrounding waters.
However, Japan has traditionally had more of a presence in the area and administers the islands.
A tense territorial row broke out in September after Japan arrested a Chinese trawler captain after a collision in the area between his boat and Japanese coastguard ships.
He was eventually freed but the dispute brought ties between the Asian neighbours to their lowest point in years.
The arrest sparked serious protests from China, which cut or dramatically reduced political, cultural and economic exchanges with Japan. The two have since worked to get their relationship back on an even keel.
After the incident, Beijing sent fishery patrol boats to the disputed waters several times, the last time on November 20 before withdrawing them last Sunday.