BEIJING - China on Monday demanded Japan immediately withdraw its fishing ships out of the waters of the Diaoyu Islands.

"China has lodged solemn representation with the Japanese side,"  Foreign Ministry spokesman Hong Lei made the remarks in reply to a question saying some Japanese boats were sent to fish in the waters of the Diaoyu Islands.

According to the Japanese media, about 10 fishing boats belonging to a fishery cooperative in Ishigaki, Okinawa Prefecture, left a local port Sunday to operate in the waters of the Diaoyu Islands, known as Senkaku in Japan.

"China has indisputable sovereignty over the Diaoyu Islands that have been an inherent part of China since ancient times," Hong said, stressing that any actions taken by Japan in the area were invalid.

It is reported that the Japanese fishing boats have already withdrawn from the Diaoyu Islands waters, Hong said, without providing a time frame.