RUDRAPRAYAG, India — Rescuers in northern India worked Monday to rescue more than three dozen power plant workers trapped in a tunnel after part of a Himalayan glacier broke off and sent a wall of water and debris rushing down a mountain in a disaster that has left at least 26 people dead and 165 missing.

More than 2,000 members of the military, paramilitary groups and police have been taking part in search-and-rescue operations in the northern state of Uttarakhand after Sunday’s flood, which destroyed one dam, damaged another and washed away homes downstream.

Officials said the focus was on saving 37 workers who are stuck inside a tunnel at one of the affected hydropower plants. Heavy equipment was brought in to help clear the way through a 1.5-mile tunnel and reach the workers, who have been out of contact since the flood.

“The tunnel is filled with debris, which has come from the river. We are using machines to clear the way,” said H. Gurung, a senior official of the paramilitary Indo Tibetan Border Police.

Authorities fear many more people are dead and were using boats to search for bodies downstream. They also walked along riverbanks and used binoculars to scan for bodies that might have been washed downstream.

The flood was caused when a portion of the Nanda Devi glacier snapped off Sunday morning, releasing water trapped behind it. Experts said the disaster could be linked to global warming, and a team of scientists was flown to the site Monday to investigate what happened. The floodwater rushed down the mountain and into other bodies of water, forcing the evacuation of many villages along the banks of the Alaknanda and Dhauliganga rivers. Video showed the muddy, concrete-gray floodwaters tumbling through a valley and surging into a dam, breaking it into pieces with little resistance before roaring on downstream.

It turned the countryside into what looked like an ash-colored moonscape.

A hydroelectric plant on the Alaknanda was destroyed, and a plant under construction on the Dhauliganga was damaged, said Vivek Pandey, an Indo Tibetan Border Police spokesman. Flowing out of the Himalayan mountains, the two rivers meet before merging with the Ganges River. The trapped workers were at the Dhauliganga plant, where on Sunday 12 workers were rescued from a separate tunnel.

A senior government official said they don’t know the total number of people who were working in the Dhauliganga project. “The number of missing people can go up or come down,” S.A. Murugesan said.

Pandey said Monday that 165 workers at the two plants, not including those trapped in the tunnel, were missing and 26 bodies were recovered. Those rescued Sunday were taken to a hospital, where they were recovering.