"If it had not been for an explosion this morning, maybe the fire would have been extinguished by now," said Hadi Haghshenas, deputy director for Iran's Ports and Maritime Organisation, in an interview with state broadcaster IRIB.
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 on Saturday.
One body has been found but 31 sailors -- mainly Iranians -- remain missing with officials in Iran hoping they have found sanctuary on an unaffected part of the vessel.
"The tanker is moving from the site of the accident, which was about 155 miles from Shanghai port, to Japanese waters and right now is about 135 miles from Okinawa Island," he said.
A Japanese coastguard spokesman said: "We offered support for efforts to deal with the accident but the Chinese side said they will handle the case by themselves."
Iranian officials have criticised China's rescue efforts, but the Chinese transport ministry said yesterday that "terrible" weather conditions and toxic gases from the burning oil were hindering operations.
A Chinese foreign ministry spokesman told AFP the government had put "a high degree of emphasis on the rescue work" and maintained "a welcoming and open attitude towards other countries coming to participate".
The 21 Chinese crew member of the Crystal, which did not burst into flames, were all rescued.