The number of trapped workers was confirmed on Monday by Rajesh Pawar, project manager at 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,” 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 tunnel is about 200 metres 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 over 600 houses because of the sinking of land in and around the town of Joshimath in the region.