Indian authorities have launched a search operation after part of a mountain glacier broke, sending a massive flood of water and debris slamming into two dams and damaging a number of homes.
At least three people were killed and 150 others were missing.
A portion of the Nanda Devi glacier broke off in the Tapovan area of the northern state of Uttarakhand on Sunday morning, damaging the Rishiganga and Dhauliganga hydropower projects, said Vivek Pandey, a spokesman for paramilitary Indo Tibetan Border Police.
Mr Pandey said at least 150 people were working at the two power plants and their fate is unknown.
He said three bodies had been recovered near a tunnel of the Dhauliganga project, where at least 16 workers remained trapped.
Government spokesman Ravi Bejaria said some houses were also damaged in the flooding.
Officials said when the glacier broke it sent water trapped behind it as well as mud and other debris surging down the mountain and into other bodies of water.
An advisory was issued urging people living on the banks of the Alaknanda River to move to safer places immediately.
Several teams of rescuers were rushed to the affected area, officials said.
The Himalayan area has a chain of power projects on the Alaknanda River and its tributaries.
In 2013, more than 1,000 people were killed in Uttarakhand after heavy rain triggered landslides and floods, washing away thousands of houses and roads and cutting communication links in many parts of the state.