Eight people were missing when mudslide flow caused by heavy rain drowned a dormitory building at a chemical plant in southwest China's Sichuan Province early Sunday, local police said.

The accident happened shortly after midnight in the suburbs of Maoxian County in the Aba-Tibetan Qiang Autonomous Prefecture, said a spokesman with the fire prevention center of Aba's public security bureau.

When rescuers arrived at the site at 12:35 a.m., the first two stories of the four-story building were drowned and dozens were stranded, he said.

The rescuers used safety ropes to divert the trapped workers to the fourth floor before helping them down to the ground, the spokesman said.

He said 27 workers were saved by 2 a.m.

Eight people were reported missing, but no bodies were retrieved at the site.

Four officers were still searching for the missing.

The local weather bureau issued an alarm for geological disasters late Saturday. The county government evacuated more than 700 villagers overnight for safety considerations.