Rescue work is on to take out the workers safely.
The fate of three labourers -- trapped since Saturday when an under-construction tunnel near Bilaspur town in Himachal Pradesh collapsed blocking the passage -- remained uncertain on Monday as rescue workers failed to reach them, officials said.
The Border Roads Organisation, an organisation under the defence ministry that has been involved in the construction of the Rohtang tunnel, was deployed for the rescue operation.
"The continuous rolling down of debris from the hilltop is hampering the rescue operation," National Highways Authority of India project director Satish Kaul told reporters.
"We are trying to insert a pipe into the debris so that the struck workers could be safely evacuated," Mr Kaul said.
Rescue workers are hopeful that the trapped workers are alive as machines have been deployed to pump oxygen into the tunnel.
The tunnel, which is part of the under-construction four-laning of the Kiratpur-Manali national highway, is located at Tihra, 13 km from district headquarters Bilaspur and 100 km from the state capital.
Workers involved in the construction work blamed the Himalayan Construction Company for lack of safety measures. All the trapped workers belonged to the hill state.
"For the past few days, huge cracks and fissures surfaced in a rock inside the tunnel. The company had been ignoring it and due to its negligence the accident occurred," one of the survivors told police.
Official sources said the cave-in took place around 8:30 pm on Saturday when workers of the night shift were coming to work. The first shift was over at 8 pm