An oil spill was discovered in north China's Bohai Sea Friday evening, according to maritime authorities.

The Tianjin branch of the China National Offshore Oil Corp. said it?spotted an oil belt near the Jinzhou 9-3 oilfield, which is operated by a subsidiary of CNOOC in the Liaodong Bay off northeast China, around 5 p.m.

The oil spill was caused by the leak from a subsea connecting pipeline damaged by a work vessel during its operations, according to?a CNOOC's statement on its website.

The company said it had taken "effective measures to clean up the oil sheen as well as sent divers to survey the damaged subsea pipeline and seal the leaking source".

Production would be cut by about 1,600 barrels per day because of the shutdown, said CNOOC.

The State Oceanic Administration (SOA) has initiated a level-three emergency response to the spill and has dispatched a plane and a monitoring vessel to assess any possible damage, said Xinhua. It did not describe the scale of the spill and said the ship was still investigating.