The wreck of an Iranian oil tanker that collided with a cargo ship off China this month has been located, Beijing said on Wednesday, but gave no new details about the environmental impact of the disaster.

The Sanchi, which was carrying 136,000 tonnes of light crude oil from Iran, ran into Hong Kong-registered bulk freighter the CF Crystal on January 6, sparking a fire that Chinese rescue ships struggled to extinguish.

It sank on Sunday after a new and massive fire erupted, sending a cloud of black smoke as high as a kilometre above the East China Sea. The bodies of only three of the 32 crew members — 30 Iranians and two Bangladeshis — have been found.

On Monday Chinese ships scrambled to clean-up a massive oil spill amid fears of devastating damage to marine life.

“The location of the wreck has been confirmed,” China's transport ministry said on its official social media platform, adding that the ship lay at a depth of around 115 metres.

Thirteen vessels were sent to continue emergency operations at the scene on Tuesday.

Next, “underwater robots will be deployed to explore the wreck waters,” the transport ministry added.

Three separate slicks were easily visible from surveillance planes, up to 18.2 kilometres (11.3 miles) in length, China's State Oceanic Administration (SOA) said in a statement Monday, according to the official Xinhua news agency.

The type of condensate oil carried by the Sanchi does not form a traditional surface slick when spilt, but is nonetheless highly toxic to marine life and much harder to separate from water.

The area where the ship went down is an important spawning ground for species like the swordtip squid and wintering ground for species like the yellow croaker and blue crab, among many others, according to Greenpeace.

It is also on the migratory pathway of numerous marine mammals, such as humpback and grey whales. In addition to the light crude oil, the Sanchi also carried a fuel tank able to accommodate some 1,000 tonnes of heavy diesel.

Takuya Matsumoto, a spokesman for Japan's coastguard said it was not yet clear how much fuel remained in the ship.

“It is difficult to give an immediate assessment of what kind of environmental impact the oil leak may leave at this point. It depends on how much fuel the ship still had inside,” he told AFP on Tuesday.

“We believe the situation is reasonably under control for now.” Alaska-based oil spill consultant Richard Steiner has slammed governments for failing to gather environmental data more quickly.

“As no one has been conducting a scientific assessment of (the environmental impact), the governments and ship owners are likely to claim, erroneously, there was limited damage,” he said.