Hundreds of military personnel were deployed in the Indian Himalayas on Monday to help find at least 125 people unaccounted for after a part of a glacier broke away, setting off a torrent of water, rock and dust down a mountain valley.
Sunday's violent surge swept away a small hydro electric project called Rishiganga and damaged a bigger one further downstream.
Most of the missing were people working on the two projects, one of the many the government has been building deep in the mountains of Uttarakhand state as part of a development push.
Rescue workers were focused on a 2.5 km (1.5 miles) long tunnel where workers were believed trapped.
Vivek Pandey, a spokesman of the Indo-Tibetan Border Police Force, said 30-35 workers were believed to be inside the tunnel and that rescuers were trying to open its mouth and get inside.
There had been no voice contact yet with anyone in the tunnel, another official said.
On Sunday 12 people were rescued from another tunnel.
Videos on social media showed water surging through a small dam site, washing away construction equipment and bringing down small bridges.
"Everything was swept away, people, cattle and trees," Sangram Singh Rawat, a former village council member of Raini, the site closest to the glacier, told local media.
Some 400 soldiers have been deployed to the site in the remote mountains, state authorities said.
"We expect to carry on operations for the next 24 to 48 hours, " said Satya Pradhan, the chief of the National Disaster Response Force.
It was not immediately clear what had set off the avalanche at a time when it is not the flood season. In June 2013, record monsoon rains in Uttarakhand caused devastating floods that claimed close to 6,000 lives.
That disaster was dubbed the "Himalayan tsunami" because of the torrents of water unleashed in the mountainous area, which sent mud and rocks crashing down, burying homes, sweeping away buildings, roads and bridges.
Uma Bharti, India's former water resources minister and a senior leader of Modi's party, criticised the construction of a power project in the area.
"When I was a minister I had requested that Himalaya is a very sensitive place, so power projects should not be built on Ganga and its main tributaries," she said on Twitter, referring to the main river that flows from the mountains.
Environmental experts called for a halt to big hydroelectric projects in the state.
"This disaster again calls for a serious scrutiny of the hydropower dams building spree in this eco-sensitive region," said Ranjan Panda, a volunteer for the Combat Climate Change Network that works on water, environment and climate change issues.
"The government should no longer ignore warnings from experts and stop building hydropower projects and extensive highway networks in this fragile ecosystem."