CNOOC Ltd is a step closer towards restarting China's largest offshore oilfield after the government's top economic planning agency approved a development plan for the Penglai 19-3, a company official said.

The oilfield, in northern Bohai Bay, was shut in September 2011 after an oil spill. The National Development and Reform Commission has now approved an overall development plan for the oilfield, one of several steps necessary to restart production, said the official who declined to be named as he was not authorised to talk to the media.

"The restart of production at Penglai 19-3 oilfield will still need to go through other government institutions and meet other requirements," the official said without giving further details.

U.S. oil firm ConocoPhillips owns a 49 percent stake in the 168,000 barrel-per-day oilfield and acts as operator, while CNOOC Ltd has a 51 percent stake.

The China's State Oceanic Administration had described the spill, which began in June 2011, as a major accident caused by negligence. It said 6,200 square km of waters had been polluted.

Operator ConocoPhillips China was ordered to halt all operations at the oilfield in September 2011 after failing to stop the leak.

ConocoPhillips and CNOOC have agreed to pay 1.683 billion yuan ($266.89 million) in compensation for the oil spill.