An oil spill by a subsidiary of ConocoPhillips has polluted 5,500 square kilometres of water in China's northern Bohai Bay, China's marine authorities and state media said on Friday, adding the company will have to pay for the spill.

The oil leak at the Penglai 19-3 oilfield, China's biggest offshore oil field, which started in June, is the most serious marine ecological incident in China, the official Xinhua news agency cited Liu Cigui, director of the State Oceanic Administration (SOA), as saying.

Seeking compensation for damage of the oil spill is a long-term, huge and complicated task, Liu told Xinhua. Any company that damages China's marine environment will pay a price.

SOA said earlier this week that it was preparing to sue ConocoPhillips over the oil spill and was ready to file a lawsuit seeking compensation once it appoints a team of lawyers, hopefully before the end of this month.

As of Tuesday, 5,500 sq km of water had been polluted, of which 870 sq km were seriously polluted, the SOA said on its website (

Six more leaking points have been found near platform C of Penglai 19-3, bringing the total number of leaking points near the platform to 16, said the North Sea branch of SOA. ConocoPhillips earlier had said the two original leaks had been sealed.

The administration has repeatedly urged ConocoPhillips China to seal off spill sources and clean up oil-based mud by the end of this month, and the company has said it was on track to do so.

If ConocoPhillips cannot fulfil these tasks in time, the administration will take strict measures, the SOA said, without providing details.

ConocoPhillips owns a 49 percent stake in the oilfield and acts as the operator, while China's top offshore oil and gas producer CNOOC Ltd has a 51 percent stake.

Oil-polluted particles found in coastlines and beaches in nearby Liaoning and Hebei provinces were partly or all from Penglai 19-3 oilfield, the SOA said.

Fishermen in Hebei province were preparing to sue the U.S. firms for allegedly wiping out large numbers of scallops in the ocean, Chinese media reported earlier.

The reports estimated that the spill had inflicted between 150 million yuan ($23.5 million) and 170 million yuan of losses on the fishing sector.

ConocoPhillips China said this week it had started evaluating the environmental impact of its oil spill, but said it had not received any claims for the incident.

Penglai 19-3 oilfield has seven production platforms, with total production of 8.4 million tonnes a year (168,000 bpd), about 20 percent of total crude oil production in Bohai Bay, the SOA said.