Four Chinese Coast Guard ships entered Japanese territorial waters near the Senkaku Islands in the East China Sea Friday evening, the Japan Coast Guard said.
The vessels were spotted entering the waters near the Japanese-controlled islands around 8:15 p.m., the 11th Regional Coast Guard Headquarters in Naha, Okinawa Prefecture said.
Ownership over the islands remains a source of tension between Japan and China, which claims the uninhabited islands and calls them the Diaoyu.
The Japan Coast Guard warned the four vessels to leave the waters but the vessels did not respond.
The intrusion was the first since Aug. 27 when three Chinese Coast Guard vessels intruded into Japanese waters and the latest in a series of intrusions since Tokyo purchased three of the islet group's five main islands from a Japanese private owner September last year.