A unit of ConocoPhillips said it has found several small oil leaks in China's northern Bohai Bay two months after an oil spill began, while the Chinese government again urged the company to halt the leak by the end of this month.

The oil leak at the Penglai 19-3 oilfield, China's biggest offshore oil field, which started in June, has polluted 840 square kilometres of water, the State Oceanic Administration (SOA) has said.

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

ConocoPhillips China is also closely monitoring and sampling several small seeps (SIC) which are appearing in a concentrated 15 meter diameter area on the sea floor approximately 15 meters north of the C Platform, the company said on its website (www.conocophillips.com.cn).

While samples are still being analyzed, it is believed the source of these seeps is residual mineral oil-based mud associated with the June 17 release that is migrating up from shallow subsurface sand layers, it said.

The company is developing plans to stop the seeps.

The official Xinhua news agency said on Saturday that ConocoPhillips had found nine sources of oil leakage on the seabed 15 metres north of platform C.

As of Sunday, ConocoPhillips China has cleaned up 369 cubic metres, or 90 percent, of oil-based mud released since the oil spill and the company expects to have the mud cleaned up completely by the end of August, in about a week and a half.

The State Oceanic Administration, together with the Ministry of Land and Resources, Ministry of Environmental Protection, Ministry of Agriculture and the National Energy Administration, on Friday urged ConocoPhillips again to take effective measures to cut oil spill sources and eliminate risks of any further oil spill, the oceanic administration said on its website (www.soa.gov.cn)

The government also asked CNOOC to shoulder its regulatory responsibility and keep the public informed about development of the oil spill.