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 a dozen people are known to have died and a further 140 others are 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.

The Rishiganga hydropower plant was destroyed, while the Dhauliganga hydropower plant was damaged, said Vivek Pandey, a spokesman for the paramilitary Indo Tibetan Border Police.

Both are on the Alaknanda River, which flows from the Himalayan mountains to the Ganges River.

Mr Pandey said at least 16 workers were trapped near a tunnel at the Dhauliganga project. Another 140 workers at the two plants were missing, he added.

Surjeet Singh, a police official, said nine bodies were recovered so far amid intensified rescue operations.

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.

Authorities emptied two dams further down the river to stop the flood waters from reaching the towns of Haridwar and Rishikesh, where popular tourist spots on the banks of the Ganges River were shut and all boating activities were stopped.

The Himalayan area has a chain of power projects on the Alaknanda River and its tributaries.

Prime Minister Narendra Modi said in a tweet he was “constantly monitoring the unfortunate situation”. He added: “India stands with Uttarakhand and the nation prays for everyone’s safety there.”

In 2013, thousands of people were killed in Uttarakhand after heavy rains triggered landslides and floods, washing away thousands of houses and roads and cutting communication links in many parts of the state.