JAPAN has warned it needs to expand its surveillance activities to cover the Pacific Ocean off its east coast to protect its interests in a zone rich with resources where Chinese naval ships were recently spotted by ministry officials.

Japan's navy and coastguard have concentrated their efforts on the Sea of Japan and the East China Sea, off its west coast, where Tokyo is locked in a territorial dispute with Beijing over a group of East China Sea islets.

The islands, called the Senkaku in Japan and Diaoyu in China, are located near rich fishing grounds and potentially large oil and gas reserves. Uninhabited, they are administered by Japan and have become a theatre for cat-and-mouse operations by patrol vessels from both sides.

Defence Minister Itsunori Onodera's comments followed observations by officials in July that Chinese naval vessels were sailing clockwise around Japan's main islands.