Six men remain trapped underground one day after an illegal coal mine in Shanxi province flooded, the local government said on Wednesday.

Liu Xianyun, a production safety official in the city of Yangquan, said water levels in the mine had dropped by just over three meters as of Wednesday morning, as rescuers have been working to pump the water out.

More than 3,100 cubic meters of water have been pumped from the coal mine, and 375 cubic meters are being pumped out every hour, Liu said.

Rescuers said their work has been difficult because of a lack of geological data.

"Water levels underground remain higher than 2 meters. Judging from the amount that has been pumped out and the current water level, water has been continued flowing into the mine," Liu said.

Rescuers will install more water pumps to speed up the process, because they cannot enter the mine to find the stranded miners until the floodwaters are completely drained, Liu said.

Medical workers are standing by to give survivors emergency treatment.

The accident occurred at about 4 am on Tuesday in Yangquan, where 12 people illegally dug a mine pit in a residential building. Six of the 12 escaped the flood.

A resident claimed that farm vehicles had been used to transport coal from the residence on Sunday evening.

The government of Yangquan has initiated a campaign to discourage illegal mining. The government is investigating similar cases and encouraging residents to report illegal mining operations.