The accident occurred at 3 a.m. Sunday at the construction site of a 14-km-long railway tunnel, the longest of 121 railroad tunnels linking Yichang City in Hubei and Wanzhou in southwest China.
The accident happened following heavy rain which caused a mudslide 240 meters away from the tunnel mouth, trapping 52 workers.
So far, 43 people have been rescued, and one person has died. Nineteen people have been hospitalized, one is in a serious condition.
Rescuers said they had been in contact with the trapped workers and their lives were not in danger.
Three water pumps have pumped out huge quantities of water, but mud and rocks have blocked parts of the tunnel where the workers are believed to be trapped.
In the past few weeks torrential rains have caused severe floods and mudslides in many parts of China, leaving hundreds dead and forcing many hundreds of thousands from their homes.