Chinese rescuers Saturday recovered two bodies and the "black box" from a stricken Iranian oil tanker which has been ablaze for the past week off the east coast of China, the transport ministry said.

The Sanchi, carrying 136,000 tonnes of light crude oil from Iran, has been in flames since colliding with the CF Crystal, a Hong Kong-registered bulk freighter, 160 nautical miles east of Shanghai last Saturday.

It had a crew of 32 -- 30 Iranians and two Bangladeshis. With the latest find a total of three bodies have now been recovered. The remaining sailors are still missing.

"At 0837 (0037 GMT), four rescuers equipped with masks and bottles of oxygen were placed at the deck at the back of the Sanchi with the help of a crane," the Chinese transport ministry said in a statement.

"They discovered the bodies of two sailors in a lifeboat."

A video released by the ministry shows rescuers wearing white helmets and orange jumpsuits walking on the tanker, whose grey metallic structure appears to have been devastated by fire.

"After recovering the black box, the rescuers tried to reach the communal areas (....) But the temperature reached 89 degrees Celsius (192 degrees Fahrenheit) and they could not enter," the ministry said.

A total of 13 vessels -- 10 Chinese, two Japanese and one South Korean -- are taking part in the rescue operation, oil recovery and firefighting.

An Iranian sailors' group has criticised China's rescue efforts, but the Chinese transport ministry said Thursday that "terrible" weather conditions and toxic gases from the burning oil were hindering operations.

"The Iranian search team will soon reach the tanker," Hadi Haghshenas, deputy director of Iran's Ports and Maritime Organisation, told the Ilna news agency on Saturday.

A day earlier, he said 12 members of the elite team were still waiting in Shanghai for conditions to allow them to go to the ship.

Operated by Iran's National Iranian Tanker Company, the Panamanian-flagged ship was transporting light crude condensate to South Korea.

The 21 Chinese crew members of the Crystal, which did not burst into flames, were all rescued.