BEIJING • An Iranian oil tanker that sank in the East China Sea has left two oil slicks covering a combined 109 sq km, the Chinese government has said, as maritime police scour the area for damage.

Satellite imaging showed a slick of 69 sq km and a second 40 sq km slick, which is less thick and not as concentrated, the State Oceanic Administration (SOA) said in a statement late on Tuesday.

The large tanker Sanchi sank on Sunday in the worst oil ship disaster for decades, raising worries about damage to the marine ecosystem.

The vessel's crew of 30 Iranians and two Bangladeshis are all believed to have died in the incident.

The SOA said vessels have taken 31 water samples in the area around the wreck containing black grease with heavy oil smells, and a concentration of petroleum that exceeds some seawater quality standard limits.

The news comes as clean-up teams continue to monitor the affected area to assess the distribution and drift of the oil spill and the ecological impact.

The tanker had been adrift and ablaze after crashing into the freighter CF Crystal on Jan 6.

Strong winds pushed it away from the Chinese coast, where the incident happened, and into Japan's exclusive economic zone.

The ship was carrying 136,000 tonnes or almost a million barrels of condensate - an ultra-light, highly flammable crude oil - and sank after several explosions weakened the hull.

REUTERS