A Chinese surveillance ship intruded into Japan's territorial waters near the disputed Senkaku Islands on Saturday for the second straight day, the Japan Coast Guard reported.

It is the 10th time a Chinese vessel has strayed into the area since Japan nationalized three islets in the Senkaku chain in September. The East China Sea isles are under Japan's control but are claimed by China, which calls them Diaoyu.

The coast guard said that after one of its patrol boats instructed the Chinese ship to immediately leave the waters, it replied that it was simply carrying out standard navigation activities.

Also Saturday, two more of China's surveillance vessels entered the contiguous zone around the Senkaku Islands, the 15th consecutive day Chinese ships have approached the uninhabited isles.

China has escalated its maritime activities around the Senkakus following Japan's Sept. 11 purchase and nationalization of the three islets, a move that sent relations between the two Asian powers into a major tailspin