The stricken NITC suezmax Sanchi 'keeps exploding', according to Chinese state news agency Xinhua on Friday.
The blasts are hampering continued rescue and firefighting efforts, it cited the ministry of transport as saying, as fears persisted the tanker could break up or sink.
Earlier on Friday it was reported the vessel had been forced away from the Chinese coast by strong winds.
Japan's coast guard told Reuters the 164,000-dwt tanker (built 2008) was now in its exclusive economic zone (EEZ).
It was in collision with a CoscoCS bulker on Saturday, causing a severe fire, an explosion and a leak of its condensate cargo.
A total of 31 of 32 crew remain missing.
China’s state-owned China Central Television (CCTV) on Friday morning said the ship had drifted about 40km to the south over the past two days.
The Japanese coast guard said it was about 300km north-west of Sokkozaki on the island of Amami Oshima as of Thursday afternoon.
Amami Oshima is one of the northern islands in the Ryukyu islands chain that includes Okinawa.
A spokesman said Chinese authorities turned down an offer from the Japanese coast guard to help, saying it would ask for help when needed.
Japan has sent patrol boats and aircraft to monitor the situation, he said. Firefighting efforts continue.
Meanwhile, The Guardian reported that criticism of the effort to locate the missing crew had been growing in Iran.
The Iranian Merchant Mariners Syndicate said it had written to Chinese authorities expressing frustration at the lack of progress in putting out the fire.
“It was clear that the Chinese are not cooperating enough,” IMMS vice-president Saman Rezaie told AFP.
And Iranian news website Khabar Online has published video interviews with some of the relatives of those missing.
“I don’t know what else to say but just beg them to rescue them as I am sure that they are alive inside,” said one woman, who identified herself as the wife of the Sanchi’s chief engineer.
