Rescuers are digging through dirt and parts of a collapsed road tunnel to reach 40 workers trapped by a landslide at a construction project in northern India.

All of the construction workers are safe, police officer Prashant Kumar said, adding that they have been supplied with oxygen and water.

He said the rescuers had established contact with the trapped employees.

The collapse occurred on Sunday in Uttarakhand, a mountainous state dotted with Hindu temples which attracts many pilgrims and tourists.

Rescuers outside the collapsed road tunnel
Rescuers outside the collapsed road tunnel (SDRF/AP)

Extensive construction of buildings and roads have taken place in recent years in Uttarakhand.

The trapped workers were building part of the Chardham all-weather road, a flagship federal government project connecting Hindu pilgrimage sites.

The number of workers trapped was confirmed on Monday by Rajesh Pawar, the project manager at the Navyug Construction Company, which is overseeing the construction of the tunnel.

Rescue efforts began on Sunday, with authorities pumping oxygen through a pipe into the collapsed section of the tunnel to help workers breathe.

“The team has progressed 15 metres into the tunnel, with an additional 35 metres yet to cover,” Mr Kumar said, adding that more than 150 rescuers had used drilling equipment and excavators to clear debris through the night.

The collapsed portion of the 4.5-kilometre (2.7-mile) tunnel is about 200 metres (500ft) from the entrance, officials told the Press Trust of India news agency.

In January, Uttarakhand state authorities moved hundreds of people to temporary shelters after a temple collapsed and cracks appeared in more than 600 houses because of the sinking of land in and around Joshimath town.