China's coast guard said it patrolled the waters of the Diaoyu Islands on Tuesday — territories in the East China Sea that are claimed by China, Japan, and Taiwan.

Japan's coast guard issued a bulletin saying it was repeatedly urging the four Chinese vessels to leave "our territorial waters." Japan calls them the Senkaku islands.

The four vessels left the waters within two hours and sailed northward, Japan's coast guard said in a later bulletin.

Chinese coast guard vessels last entered the waters Jan. 27, it added.