HARBIN, Oct. 10 (Xinhua) -- The death toll in a colliery fire that occurred on Sept. 22 in northeast China's Heilongjiang Province has risen to 12, as rescuers found one more body from the razed-down mine shaft debris on Wednesday.

The rescue headquarters said the rescue efforts have been hampered by falling ceilings and dense concentration of inflammable gas in the shaft.

Investigators said there were 14 miners working in the pit when the fire broke out at 11 a.m. in the No. 10 pit of Longshan Coal Mine in Shuangyashan City. Only two of them escaped the accident.

Previous reports said there were 13 miners working at the time of the accident and 11 of them were trapped. Investigators said they have found there was another worker who entered the pit without leaving his access record.

The cause of the accident is still under investigation.