An off-shore oil rig has leaked and spread oil over about one square kilometer off China's northeast coast, the third oil spill in the area in less than two months.

The State Oceanic Administration says the leak occurred in the Suizhong 36-1 oil field, operated by China National Offshore Oil Corporation, in the region known as the Bohai Sea. CNOOC is one of the nation's largest oil producers.

State media quote the oceanic administration as saying the company is working to clean up the spill.

Last month, two leaks from rigs in another CNOOC oil field spread over more than 840 square kilometers. State media and environmental groups criticized CNOOC, and its partner in the oil field, ConocoPhillips China, because they did not report the leak for more than a month.