As many as 150 people were feared dead after a Himalayan glacier broke and crashed into an Indian dam early on Sunday, with floods forcing the evacuation of villages downstream.
"The actual number has not been confirmed yet," but 100 to 150 people were feared dead, Om Prakash, chief secretary of Uttarakhand state where the incident happened, told Reuters.
An eyewitness in said he saw a wall of dust, rock and water as an avalanche roared down a river valley.
"It came very fast, there was no time to alert anyone," Sanjay Singh Rana, who lives on the upper reaches of Raini village, told Reuters by phone. "I felt that even we would be swept away."
Locals fear that people working at a nearby hydro-power project had been swept away, as well as villagers roaming near the river looking for firewood or grazing their cattle, Rana said.
"We have no idea how many people are missing," he said.
India has also put many of its northern districts on high alert.
Footage shared by locals showed the water washing away parts of the dam as well as whatever else was in its path.
Videos on social media, which Reuters could not immediately verify, showed water surging through a small dam site, washing away construction equipment.
"The flow of the Alaknanda River beyond Nandprayag (stretch) has become normal," Uttarakhand Chief Minister Trivendra Singh Rawat said on Twitter.
"The water level of the river is now 1 meter above normal but the flow is decreasing."
Uttarakhand in the Himalayas is prone to flash floods and landslides. In June 2013, record rainfall caused devastating floods that claimed close to 6,000 lives.
That disaster was dubbed the "Himalayan tsunami" by the media due to the torrents of water unleashed in the mountainous area, which sent mud and rocks crashing down, burying homes, sweeping away buildings, roads and bridges.