Rescuers searching ravines and valleys for survivors after the sudden collapse of a Himalayan glacier triggered massive flooding in northern India have found 11 more bodies.

The grim discovery raises the death toll from the incident in northern India a week ago to 49.

Krishan Kumar, a spokesman for the National Disaster Response Force, said 155 people were still missing after part of a glacier near the Nanda Devi mountain broke off on February 7, unleashing a devastating flood across the region in Uttarakhand state.

Mr Kumar said five bodies were found in a tunnel of a power project as rescuers cleared the debris and looked for any survivors. Six other bodies were found in a village in the area.

Rescuers are using excavators and shovels to clear sludge from the tunnel in an attempt to reach dozens of trapped workers as hopes for their survival fade.

The floodwaters, mud and boulders roared down the mountain along the Alaknanda and Dhauliganga rivers, breaking dams, sweeping away bridges and forcing the evacuation of many villages.

The floodwaters swept away a small hydroelectric project and damaged a bigger one downstream on the Dhauliganga. Flowing out of the Himalayan mountains, the two rivers meet before merging with the Ganges River.

Scientists are investigating what caused the glacier to break - possibly an avalanche or a release of accumulated water. Experts say climate change may be to blame since warming temperatures are shrinking glaciers and making them unstable worldwide.