Two Chinese patrol ships detected a Japan Coast Guard vessel in the waters near the Diaoyu Islands during a routine patrol on Friday, according to a statement by the State Oceanic Administration.

But the Japanese ship didn't respond to an inquiry sent by the Chinese ships and the two Chinese ships followed the Japanese ship to track its movement, the agency said.

The statement said the patrol showed China's indisputable sovereignty over the Diaoyu Islands and its adjacent islets in the East China Sea.