Seven people were reported dead and at least 125 people are missing in northern India after a piece of Himalayan glacier fell into a river, causing a torrent that buried two power plants and swept away roads and bridges, officials said on Sunday.

The flood was caused when a portion of the Nanda Devi glacier broke off in the Tapovan area of the northern state of Uttarakhand on Sunday morning, sending flood waters crashing through the Dhauliganga river valley, destroying the Rishiganga hydropower plant on the Alaknanda River, and damaging the Dhauliganga hydropower as well as villages and homes in the area.

Flowing from the Himalayan mountains, the Alaknanda and Dhauliganga rivers meet before merging with the Ganges River.

"Seven bodies have been recovered from the site and rescue operations are going on," Uttarkhand Chief Minister Trivendra Singh Rawat told reporters in the state capital, Dehra Dun.

Around 125 people are missing and that number is likely to rise more, said Rawat.

Most of those missing were workers at the two power plants. Twelve workers trapped inside a tunnel at the Dhauliganga project were rescued and provided first aid, said Vivek Pandey, a spokesman for paramilitary Indo-Tibetan Border Police. Another 140 workers at the two plants were missing, he added.

Video clips shared on social media taken from the side of steep hillside Sunday morning showed a wall of water surging into one of the power plants, breaking it into pieces with little resistance before continuing to roar downstream.

"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."

With the main road washed away, the tunnel was filled with sludge and rocks, and rescuers were forced to climb down a hillside on ropes to gain access to the entrance.

Hundreds of troops and paramilitaries along with military helicopters and other aircraft have been sent to the region. Teams of glaciologists would also head to the area on Monday to study the causes of the disaster, according to local media reports.

Authorities emptied two dams to stop the flood waters reaching the Ganges at the towns of Rishikesh and Haridwar, where authorities barred people from going near the banks of the river, officials said.

Prime Minister Narendra Modi said he was closely monitoring the situation.

"India stands with Uttarakhand and the nation prays for everyone's safety there," he said on Twitter after speaking with the state chief minister.

The neighbouring state of Uttar Pradesh, India's most populous, also put its riverside areas 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 metre 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.

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 mountain.

(FRANCE 24 with AFP and REUTERS)

Originally published on France24