Naha, Okinawa Pref., Oct. 20 (Jiji Press)–Four Chinese coast guard ships sailed in Japanese territorial waters off the Senkaku Islands in the East China Sea for about two hours on Wednesday.

It was the 30th intrusion into the Japanese waters around the island chain in Okinawa Prefecture by Chinese government ships this year, and the first since Sept. 19.

The Japanese-administered islands are claimed by China, which calls them Diaoyu.

The four Haijing ships entered the Japanese waters between about 10 a.m. (1 a.m. GMT) and 10:10 a.m. and left the areas between around 11:35 a.m. and noon, according to the Japan Coast Guard’s 11th regional headquarters in Naha, the capital of the southernmost prefecture.