The Chinese marine surveillance fleet — Haijian 51, 23, 49 and 5001 — is patrolling waters near the Diaoyu Islands on Monday, according to a statement released by the State Oceanic Administration.

The statement said that the fleet detected Japanese ships during the patrol that illegally entered Chinese waters and recorded their illegal behavior.

China's Ocean Development Report of 2013 said the possibility of conflict between China and Japan over the Diaoyu Islands is increasing.

China has carried out consistent patrols near the Diaoyu Islands since September when Tokyo "illegally purchased" three of the islands. The State Oceanic Administration will release details of the ongoing patrol on its website.