Iran said on Friday that a fresh explosion on a stricken oil tanker was complicating rescue efforts as Japan reported the vessel had drifted into its exclusive economic zone.
"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 last 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.
Haghshenas said a 12-member elite rescue team had been dispatched from Iran but was waiting in Shanghai for conditions that would allow them to land on 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.
Japan said it had provided a patrol boat because the tanker was now in its exclusive economic zone, while Iran requested helicopters and planes to help put out the fire.
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 Thursday 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".
Haghshenas said two fire emergency consultants from the Netherlands and Germany had also been hired "who are now at the scene giving advice to the Chinese".
The 21 Chinese crew member of the Crystal, which did not burst into flames, were all rescued.