Rescuers in southern China were racing against time on Monday to reach more than 40 coal miners trapped underground at the weekend in two flooded pits, state media said.
In the southern Guangxi region, heavy rains hampered efforts to reach 19 workers trapped in a colliery in Heshan city which collapsed on Saturday due to torrential downpours pummelling the area, Xinhua news agency reported.
Three bodies have already been pulled from the pit, the report said.
"The density of the toxic gas in the mine shaft remains high, and we have to be wary of more collapses," rescue worker Huang Xiangxiong told the agency.
In the neighbouring province of Guizhou, 23 miners were trapped in another mine that flooded on Saturday due to heavy rains and a breakdown in the shaft's drainage system. Most of the workers hail from Guangxi.
Xinhua cited the local emergency rescue headquarters as saying water levels had dropped by two metres (six feet) late Sunday, but then quickly rose again.
Rescuers worked through the night to pump water out of the pit, Xinhua said, adding that more pumps were due to be installed on Monday to help speed the process.
Li Shangkuan, the deputy chief of Guizhou's work safety administration, vowed a thorough investigation into the incident.
China's coal mines have a notoriously poor safety record, which the government has repeatedly pledged to address.
In its latest campaign, the government issued a policy last year that required six kinds of safety systems, including rescue facilities, to be installed in all coal mines within three years.
In 2010, 2,433 people died in coal mine accidents in China, according to official statistics, or a rate of more than six workers per day.
Labour rights groups, however, say the actual death toll is likely much higher than official data indicates, partly due to under-reporting of accidents as mine bosses seek to limit their economic losses and avoid punishment.