An Iranian oil tanker collided with a bulk freighter and caught fire off China's eastern coast, leaving its entire crew of 32 missing, most of them Iranians, authorities said Sunday.

The missing 30 Iranians and two Bangladeshis are all from the tanker Sanchi, which spilled oil and was floating while still burning early Sunday, said Chinese maritime authorities, who dispatched police vessels and three cleaning ships to the scene.

Chinese state media carried pictures of the tanker on fire with smoke plumes daytime Sunday.

The South Korean coast guard also sent a ship and an airplane to aid the search effort.

The Panama-registered tanker was sailing from Iran to South Korea when it collided with the Hong Kong-registered freighter CF Crystal 257 kilometres off the coast of Shanghai late Saturday, the Ministry of Transport said.

All 21 members of the Crystal's crew ─ all Chinese nationals ─ were rescued, the ministry said.

It wasn't immediately clear what caused the collision.

The Sanchi was carrying 136,000 metric tons (150,000 tons) of condensate, a type of ultra-light oil, while the Crystal was carrying grain from the United States, according to Chinese authorities.

The size of the oil slick caused by the accident was not immediately known.

The tanker has operated under five different names in the time since it was built in 2008, according the UN-run International Maritime Organization. The IMO listed its registered owner as Hong Kong-based Bright Shipping Ltd., care of the National Iranian Tanker Co, a publicly traded company based in Tehran.

The National Iranian Tanker Co. describes itself as operating the largest tanker fleet in the Middle East.

An official in Iran's Oil Ministry, who spoke to The Associated Press on condition of anonymity because he was not authorized to speak to reporters, said 30 of the 32 crew members on the ship were Iranians.

“We have no information on their fate,” he said. “We cannot say all of them have died, because rescue teams are there and providing services.”

He said the tanker was owned by the National Iranian Tanker Co., and had been rented by a South Korean company, Hanwha Total Co. He said the tanker was on its way to South Korea.

Hanwa Total is a 50-50 partnership between the Seoul-based Hanwha Group and the French oil giant Total. Total did not immediately respond to a request for comment.

It's the second collision for a ship from the National Iranian Tanker Co. in less than a year and a half.

In August 2016, one of its tankers collided with a Swiss container ship in the Singapore Strait, damaging both ships but causing no injuries or oil spill.