Since then, the Panama-registered tanker Sanchi has been ablaze and drifting in the waters between Shanghai and southern Japan.
The 21 Chinese crewmembers of the Crystal, which did not burst into flames, were all rescued.
Two vessels collided off China's east coast Saturday evening and 32 sailors, 30 Iranians and two Bangladeshis, are still missing.
The Sanchi "is floating and burning as of now", the Chinese Transportation Ministry said Monday.
A safety data sheet by the oil company ConocoPhillips said that condensate "may be fatal if swallowed and enters airways" and is "toxic to aquatic life with long-lasting effects".
China has assisted 12 Iranian rescue workers to arrive at Shanghai and arranged them to participate in search work, a Chinese Foreign Ministry spokesperson said on Friday.
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Even after parts of it exploded, and while it's still on fire, an Iranian diplomat said Thursday the crew on the oil tanker Sanchi may yet be alive.
Chinas largest patrol ship Haixun 01 is fighting the fire after the explosion while organising other vessels to move away, the ministry said.
Amid fears the tanker could break up and sink, dozens of rescue boats have doused the vessel with foam.
It collided with the freighter CF Crystal (IMO:9497050) that was carrying grain from the United States about 160 nautical miles (184 km) off China's coast near Shanghai. In March 1989, the Exxon Valdez oil tanker ran aground in Alaska's Prince William Sound, spilling 10.8 million gallons of crude oil, devastating herring and salmon runs and causing one of the worst environmental disasters in US history. "This produces a very toxic plume of water which, unlike most crudes, won't decay through microbial action in the same way".
Experts are especially anxious because the ship is carrying condensate, an ultralight version of crude oil.
After meeting with a special investigatory committee formed by Iranian President Hassan Rouhani, its spokesman, Mohammad Rastad, said that poisonous gas, Wednesday's explosion and oil pollution were complicating the response.