The blaze was ignited around 9:44 a.m. (0144 GMT) on Wednesday by a stray spark caused by a worker performing maintenance on a water tank at the refinery's sulfur recovery workshop, said Zou Ling, an official at the provincial Work Safety Bureau said.
Zou said the blaze was extinguished in about an hour, but only two bodies were recovered. Rescuers believe the other five may have been overcome by fumes and fallen into a massive tank of highly toxic sulfurated hydrogen, she said. Workers are draining the tank, but the process is expected to take until Friday.
``We think they're in the tank but have to be very careful in dealing with the solution so that no rescuers are hurt,'' Zou said.
Daqing, located on the frozen plaints of Heilongjiang province in the far northeast, was long known as China's premier oil production base. Mao, communist China's founder, praised the town and its oil fields as a model to emulate, inventing the slogan ``in industry, learn from Daqing.''
But its known reserves have been largely pumped dry and output last year slid to a 27-year low. Tens of thousands of workers have been laid off by the oil wells and refinery, prompting a spate of large street protests.
China has been lobbying Russia to build an oil pipeline to Daqing in hopes of keeping its processing facilities running and reviving the town's fortunes. Russia has yet to commit, though, and is also mulling a competing Japanese proposal to build a pipeline to the Russian Far East on the Sea of Japan.
