A cloudburst over Lhonak Lake triggers flooding in a valley located in northeastern Sikkim state.

The rain lashed a valley about 150km (93 miles) north of Gangtok, located along the border with China.

“Due to sudden cloud burst over Lhonak Lake in North Sikkim, a flash flood occurred in the Testa River … 23 personnel have been reported missing,” the army said in a statement on Wednesday. “Search operations are under way.”

A defence spokesperson based in Guwahati in the neighbouring Assam state said, “Some army establishments along the valley have been affected.”

Rising water submerged some vehicles following the release of water from a dam, the spokesperson said.

The remote area lies close to India’s border with Nepal, and Lhonak Lake sits at the base of a glacier in the snowy peaks that surround Kangchenjunga, the world’s third-highest mountain.

The army said water released upstream from the Chungthang dam meant the river was already more than 4.5 metres (15 feet) higher than usual.

About 15,000 people living in the vicinity are likely to be affected and at least eight major bridges have been washed away along the banks of the Teesta River, VS Pathak, chief secretary of the state, told Reuters news agency.

A video released by an Indian army spokesperson showed a thick torrent of raging brown water sweeping down a thickly forested valley, with roads washed away and power lines ripped down.

India’s weather department has warned of landslides and disruption to flights as heavy rain is predicted in some parts of Sikkim.

Flash floods are common during the monsoon season, which begins in June and normally withdraws from the Indian subcontinent by the end of September. By October, the heaviest of the monsoon rains are usually over.

Experts say climate change is increasing their frequency and severity.

Streets swamped

Other photographs shared by the army showed water submerging the first floor of buildings and flowing down a street in a town with only the tip of a small construction crane visible poking out.

Local media showed Sikkim Chief Minister Prem Singh Tamang holding an umbrella during a downpour and talking to officials about floods in the town of Singtam, further downstream from where the soldiers are missing.

The monsoon occurs when summer heat warms the landmass of the subcontinent, causing the air to rise and suck in cooler Indian Ocean winds, which then produce enormous volumes of rain.

But it also brings yearly destruction in the form of landslides and floods.

Melting glaciers add to the volume of water while unregulated construction in flood-prone areas exacerbates the damage.

Due to climate change, Himalayan glaciers are melting faster than ever, exposing communities to unpredictable and costly disasters.

Glaciers disappeared 65 percent faster from 2011 to 2020 compared with the previous decade, a report in June by the International Centre for Integrated Mountain Development (ICIMOD) warned.

Based on current emissions trajectories, the glaciers could lose up to 80 percent of their current volume by the end of the century, it said.