At least seven people were killed and more than 170 people are missing after a glacier burst, triggering flash floods in India's northern Uttarakhand state on Sunday.

Some workers could be trapped in a tunnel at a state-owned NTPC hydro project, clogged with debris from the avalanche triggered by the glacial burst, Chief Minister Trivendra Singh Rawat said at a press conference late on Sunday evening.

"Uttarakhand has witnessed a terrible disaster," Rawat said, adding that the state is expecting "significant loss to human lives and infrastructure."

Indian Army and members from India's National Disaster Response Force (NDRF) have been assisting rescue efforts, and more NDRF teams are being airlifted from New Delhi and expected to arrive on Monday.

The Rishiganga power project, in the Chamoli district of Uttarakhand, was damaged by the floods. Those living alongside the Alaknanda River were urged to flee to safety, but stay calm.

The minister said of the total 35 people working at the Rishiganga Power project, "roughly 29 to 30 people are missing."

Some 5 kilometers from that project, flash floods affected the downstream hydro project of NTPC, a state-owned power company on the Dhauliganga river, Rawat said. Some 176 laborers were working on that project, which has two tunnels, the minister said.

"Roughly 15 people" managed to get out of one tunnel after getting word of the avalanche on their mobile devices, Rawat said, adding that 35 to 50 workers had been rescued and returned to the NTPC plant.