The Iranian oil tanker Sanchi exploded and sank on Sunday afternoon, after burning for more than a week on the East China Sea. Rescue workers earlier collected the vessel's black box and experts are looking into the cause of collision. CGTN's Ma Ke has the story.

There's almost nothing left of the oil tanker Sanchi, save for ten square kilometers of water on fire and black smoke burning up to three kilometers into the sky.

Rescue workers have recovered the bodies of only three crew members. The other 29 remain missing. Our reporter Li Jianhua at the Shanghai Maritime Bureau earlier on Sunday, said rescue operations will continue.

LI JIANHUA SHANGHAI "Three bodies have been found and two of them were returned to Shanghai and then a black box has also been retrieved. We are now still waiting for the information after the assessment of the box. Chinese authorities the Chinese foreign minister Wang Yi earlier said that China will do whatever it can as long as there is a slice of hope."

Sanchi had 32 crew members on board, 30 Iranians and two Bangladeshis. On January 6th, it collided with Hongkong freight ship CF Crystal on the East China Sea, and caught fire. Sailors on board the Chinese ship were all rescued.

Over a dozen Chinese vessels, as well as two South Korean ships, were dispatched but rescue operations were hampered due to bad weather and the fierce fire. Rescue workers for days searched the waters nearby till before the Sanchi exploded and sank on Sunday afternoon .

YANG LITIAN CCTV REPORTER "We can see Sanchi tanker has completely sunk. Nothing but debris and oil are still burning. A 10-square kilometers oil belt has been formed. It was only three-square kilometers two days ago. It is a very serious situation."

Investigation into the collision is underway, but environmental experts are more worried about the aftermath.

TENG DA CHINESE OCEANIC ADMINISTRATION "This is a rather severe marine accident I have come across in my career. Now the tanker has sunk, what comes next to the ecological system, the government should watch closely. They could face oil spill and deal with toxic materials emission."

The sunken oil tanker was carrying almost one million barrels of condensate -- a highly-flammable oil-based fuel. It evaporates quickly when exposed to air but an explosion has the potential to produce much more toxic fumes which will cause respiratory problem. Furthermore, there's the risk of the ship's own fuel leaking as well. 3 ships have been deployed for clean-up and containment work, but it is unclear how much condensate has been spilled.