HARBIN - Dense gas has hindered rescue efforts for 11 miners who became trapped after a fire broke out at a coal mine shaft in Northeast China's Heilongjiang province Saturday.

After two days of rescue efforts, rescuers have been unable to reach the miners due to a dense concentration of carbon monoxide in the shaft, said Wang Ju, chief of the Coal Mine Management Bureau of Shuangyashan city, on Sunday.

The fire is ablaze and the rescue headquarters have ordered rescuers to retreat.

Wang said rescuers are trying to dig a new tunnel to ventilate the shaft and reach the trapped.

Experts believe air and water access is available at where the miners are trapped, and there are chances that they are still alive.

Fire broke out at around 9 am Saturday when 13 miners were working at a shaft of the Longshan coal mine in Youyi County of Shuangyashan. Two of them managed to escape.

The cause of the accident is under investigation.