Heavy rainfall and drainage system breakdown are blamed for a coal mine flooding that trapped 23 workers underground Saturday in southwest China's Guizhou Province, local authorities said Sunday.

The accident happened at 9:30 a.m. Saturday at Niupeng Mine in Pingtang County of the Bouyei-Miao Autonomous Prefecture of Qiannan.

Shortly after the accident, mine authorities confirmed 21 workers were trapped. But two others were found missing Sunday and were believed to have entered the pit.

The emergency rescue headquarters said the underground water level has been briefly dropped by two meters at around 7 p.m. Sunday but then rose again.

Initial investigation shows that the water level in Hanglong river surrounding the mine increased by 2.5 meters due to recent rainfall, which caused ground water level to rise and flooded the mine, said Yang Chaohui, chief engineer of the provincial Water Resources Department.

The mine's drainage system had a breakdown on Saturday, so the miners went down the shaft to check the machines and then the mine was flooded, Yang said.

Before the flooding, the water leak in the mine was already very serious since 16 pumps, each with a drainage capacity of 900 cubic meters per hour, were used then to drain water, said Li Shangkuan, deputy chief of the provincial Work Safety Administration.

The serious water leakage should have alerted the mine managers. People responsible for the accident will be identified after thorough investigation, Li said.

Rescuers worked through the night to pump water from the pit. By 9 a.m. Sunday, 23,000 cubic meters of flood water had been drained, said Wang Jinzhong, an official from State Administration of Work Safety.

It is estimated that about 60,000 cubic meters of water have flooded into the mine in one day, which means that rescuers have to drain at least 2,500 cubic meters of water per hour to drop the water level, the rescue headquarters said.

At present 1,350 cubic meters of water are being pumped out hourly, which has already briefly lowered the water level. The drainage capacity is expected to reach 2,000 cubic meters per hour on Monday when more pumps are installed, the rescue headquarters said.

However, risks exist if more water are being drained at a faster speed.

The lowering ground water level in the mine will cause surrounding water to flow faster into the mine or even gushing out, which will threaten the rescuers underground, the rescue headquarters said.

The majority of the trapped miners are from the southern Guangxi Zhuang Autonomous Region. Family members began arriving Sunday morning to wait for news.

The local government has mobilized 500 people to receive and console the grieved family members.

Saturday saw a coal mine disaster in Guangxi, where three were confirmed dead and 19 remained stranded following a cave-in.

Rescuers are still digging into the shaft Sunday, hoping to reach the missing workers.

But high levels of explosive gas and siltage in the shaft hindered rescue efforts and little progress was reported.