A senior police official said a survivor had told him about 75 to 80 people were in the tunnel when it started to collapse late Monday. He could not say how many people had managed to escape and how many were still trapped inside.

Police overnight pulled out the bodies of nine workers, while two others were retrieved Tuesday morning, he added.

The tunnel is part of a controversial hydro-electric power project which environmentalists say is dangerous as it is being built in an earthquake prone region.

Local district official Puneet Kansal told Aaj Tak television news channel that labourers were working in the tunnel when earth started falling from the roof.

"Some people came out when the loose earth started falling but others stayed behind," he said, without giving figures.