An oil slick fire has burned out after an Iranian tanker sank in the East China Sea, although concerns remain about possible major pollution to the sea bed and surrounding waters, Chinese officials said.

Footage showed huge clouds of thick smoke rising from the oil slick that had been burning for more than a week aboard the Sanchi.

Just three bodies from the tanker’s crew of 32 – 30 Iranians and two Bangladeshis – have been recovered.

The cause of the collision on January 6 between the Sanchi and the Chinese freighter CF Crystal, which happened 160 miles east of Shanghai, remains unclear.

All 21 crewmembers aboard the freighter were reported safe.

Concerns remain about possible major pollution to the sea bed and surrounding waters (Chinese transport ministry/AP)
Concerns remain about possible major pollution to the sea bed and surrounding waters (Chinese transport ministry/AP)

Rescuers boarded the Sanchi on Saturday morning to recover two bodies, but a large explosion shook the ship around noon on Sunday and it sank within hours.

High temperatures had prevented rescuers from entering the crew quarters. Another body was recovered from the water earlier last week.

The ship was carrying a type of hydrocarbon liquid known as natural gas condensate and left a 3.8-square-mile area contaminated with oil, according to Chinese authorities.

Condensate is highly toxic but readily evaporates or burns off in a fire. If trapped underwater, however, it could seriously harm the marine environment, while the ship’s fuel source also poses a major threat.

The ship’s voice data recorder, which functions like a “black box” on aircraft, was reportedly recovered on Saturday, possibly helping shed light on how the collision and resulting fire occurred.