The tanker Sanchi (IMO:9356608), run by Iran's top oil shipping operator, National Iranian Tanker Co, collided with the CF Crystal (IMO:9497050), carrying grain from the United States, about 160 nautical miles off China's coast near Shanghai and the mouth of the Yangtze River Delta.
The Sanchi was carrying 136,000 tonnes of condensate, an ultra-light crude oil that becomes highly volatile when exposed to air and water, to South Korea.
The size of the oil spill from the ship and the extent of the environmental harm were not known, but the disaster has the potential to be the worst since 1991 when 260,000 tonnes of oil leaked off the Angolan coast.
Chinese state media CCTV showed footage on Monday of boats dousing the flames with water as plumes of thick dark smoke continued to billow from the tanker.