At least 10 workers were killed and over a dozen trapped inside a tunnel in the Indian Himalayas after a methane explosion set off a landslide that sealed its entrance, cutting off their escape.
Twenty five people were caught in the tunnel, part of an under-construction hydropower dam in Sikkim, a small mountainous state wedged between Nepal, Bhutan and China in India’s northeast.
The explosion occurred around midday on Monday at the Teesta Stage VI hydroelectric project in Namchi district, run by the state-owned National Hydroelectric Power Corporation. A build-up of methane some 1.5km inside the tunnel reportedly ignited during an attempt to vent the gas, triggering the collapse. Some workers escaped in the moments after the explosion, but several were left stranded deep underground.
Rescuers faced high concentrations of methane, low oxygen and poor visibility as they pushed through a narrow passage and several of them fell ill during the operation. “Carbon monoxide has been detected inside and visibility is extremely poor,” National Disaster Relief Force deputy commandant Vivek Kumar told the PTI news agency.
“Our team has been carrying out search and rescue operations since 5pm yesterday,” he added. “So far, we have recovered the bodies of 10 victims from inside the tunnel and the operation is still underway.”
An initial rescue attempt by local firefighters was abandoned after they struggled to breathe, and a subsequent push by the National Disaster Response Force also failed to make progress. A specialist team with breathing gear was then brought in from the neighbouring state of West Bengal to run the operation and personnel from the state disaster management authority were deployed overnight to assist.
Methane can accumulate naturally in rock as tunnelling cuts through underground strata. Colourless and odourless, the gas displaces oxygen and ignites easily, making it a primary hazard of underground construction activity.
The Teesta Stage VI is one of a series of large hydropower projects built along the river of the same name, which runs down the Himalayas through Sikkim and into West Bengal. The dams have come to become central to India’s push for renewable energy, but the fragile, earthquake-prone terrain has repeatedly proved dangerous.
In October 2023, a glacial lake high in the mountains burst and sent a wall of water down the Teesta, destroying a dam at Chungthang and killing at least 40 people. That disaster damaged infrastructure across the state and drew warnings from scientists about the risks of building on unstable Himalayan slopes.
Tunnel accidents are a recurring feature of India’s fast-moving construction sector. In February last year, a section of a canal tunnel collapsed in the southern state of Telangana, trapping eight workers.
It took many weeks to recover the bodies of the victims.
Rescue operations at the Teesta tunnel were continuing on Tuesday for the second day, with multiple state and federal agencies involved.
