A catastrophic construction accident has left at least 12 workers dead and 13 others trapped deep underground after a methane-fueled gas explosion triggered a partial collapse of an under-construction hydropower tunnel in India’s Himalayan northeastern state of Sikkim, official authorities have confirmed. As of Wednesday, multi-agency rescue operations have entered their third day, with teams focusing their efforts on a 200-meter target zone inside the tunnel where remaining trapped workers are believed to be located.
The incident unfolded on Monday around 1.5 kilometers (0.9 miles) inside the tunnel, which is being developed as part of a major hydropower project by state-owned utility National Hydroelectric Power Corporation (NHPC). Designed to divert water from the nearby Teesta River to feed the hydropower plant’s turbines, the project is a key infrastructure initiative for the mountainous state.
In an official statement following the accident, NHPC confirmed the blast was caused by a sudden outburst of methane gas naturally trapped within surrounding rock formations. The explosion generated thick toxic fumes that have complicated rescue efforts, a conclusion echoed by the Sikkim state government, which formally attributes the incident to methane gas combustion. A senior government official explained that methane naturally accumulates in underground rock formations; when tunneling work releases the gas into the confined space of the tunnel, even a small spark or other ignition source can trigger a catastrophic explosion or ignition.
At the time of the blast, 27 workers were spread across different work sections inside the tunnel. Only two workers managed to escape immediately after the explosion, leaving 25 trapped. “Of the 25 people who were trapped, we have recovered 12 bodies so far, and teams are working to locate the 13 other men,” Sonam D Bhutia, Superintendent of Police of Sikkim, told the BBC in an interview Wednesday morning. So far, authorities have confirmed the identities of seven of the deceased: one victim was a resident of Sikkim, while the remaining six identified victims are migrant workers from neighboring Indian states of West Bengal, Uttarakhand and Assam. Official confirmation of the exact cause of death for each victim will be released following full post-mortem examinations, according to authorities.
National Disaster Response Force (NDRF) officer Mohsen Shahedi told Indian news agency ANI that search and rescue teams are currently concentrating their operations on a specific 200-meter stretch of the tunnel, where modeling and on-site data suggest the remaining trapped workers are most likely located. In response to the disaster, Sikkim Chief Minister Prem Singh Tamang has ordered the formation of a specialized independent investigation team to probe the root causes of the incident. “We have engaged a team of experts to find out what exactly happened and how. We will take action on the basis of the findings,” Tamang told reporters following the disaster.