Rescuers deliver relief supplies to the collapsed coal mine in Heshan, southwest China's Guangxi Zhuang Autonomous Region, July 4, 2011. A coal mine in Heshan collapsed on July 2 after days of heavy rainfall, killing three people and trapping 19 others. Rescuers were forced to suspend parts of the relief work due to high toxic gas density. (Xinhua/Huang Xiaobang)

After carbon monoxide gushed out of the mine at 2:45 a.m., the rescue command center ordered the rescuers to retreat to the platform of the main shaft, said Ye Fangyong, an expert from the command center.

Ye added that other toxic gas in the mine is also over the safety level.

As of 9:30 a.m., the command center was still trying to identify the source of the carbon monoxide and find a solution to recommence the rescue operation. Ye said the rescue will resume as soon as possible.

The collapse occurred midday Saturday in the suburbs of Heshan City in Guangxi Zhuang Autonomous Region. Initial investigations indicate that the collapse was caused by continuous heavy rains.

Forty-nine of 71 miners managed to escape when the coal mine collapsed, and rescuers have retrieved three bodies of the dead miners.

The location of the trapped miners has been identified, but their conditions are unclear, according to the rescuers.