Nine bodies have been recovered, Surjeet Singh, a police official told the Associated Press, and a desperate operation has been launched to rescue some 17 people trapped in a tunnel.
A portion of the Nanda Devi glacier broke off in Uttarkhand state's Tapovan area on Sunday morning, damaging the Rishiganga and Dhauliganga hydropower projects as well as homes in the area.
The massive burst of water tore through the Dhauliganga river valley, destroying everything in its path, videos shot by terrified residents showed.
'There was a cloud of dust as the water went by. The ground shook like an earthquake,' local resident Om Agarwal told an Indian TV station.
Most of those missing are workers at two power plants that were battered by the deluge after a huge chunk of the Nanda Devi glacier slipped off a mountainside further upstream, the Uttarkhand state police chief Ashok Kumar said.
'There were 50 workers at Rishi Ganga plant and we have no information about them. Some 150 workers were at Tapovan,' he added.
'About 20 are trapped inside a tunnel. We are trying to reach the trapped workers.'
Vivek Pandey, a spokesman for the paramilitary Indo Tibetan Border Force said the Rishiganga hydropower plant was destroyed, while the Dhauliganga hydropower plant had been damaged.
Both are on the Alaknanda River, which flows from the Himalayan mountains to the Ganges River.
With the main road washed away, the tunnel was filled with mud and rocks and paramilitary rescuers had to climb down a hillside on ropes to get access to the entrance.
Hundreds of troops and paramilitaries along with military helicopters and other aircraft have been sent to the region to conduct rescue efforts.
Authorities have emptied two dams to stop the flood waters reaching the Ganges at the towns of Rishikesh and Haridwar, where people were barred from going near the banks of the sacred river, officials said.
