Three Chinese maritime surveillance vessels entered Japanese territorial waters on Friday near the Senkaku Islands, a Japanese-controlled islet group claimed by China, the Japan Coast Guard said.
The three vessels -- the Haijian 23, 49 and 51 -- entered Japanese waters in the East China Sea at around 9:25 a.m. from north-northwest of Kuba Island in the Senkaku group, according to the 11th Regional Coast Guard Headquarters in Naha, Okinawa Prefecture.
The coast guard said it was warning the ships to leave the area.
The intrusion prompted Shinsuke Sugiyama, director general of the Japanese Foreign Ministry's Asian and Oceanian Affairs Bureau, to lodge a protest by telephone with Han Zhiqiang, minister at the Chinese Embassy in Japan.
Chinese vessels last entered Japanese waters on May 26.
The incident on Friday was the 47th intrusion since last September, when the Japanese government purchased the majority of the Senkakus from a Japanese owner, drawing protests from China, which calls the isles Diaoyu.