Fifteen Indian workers remain trapped following an explosion at a hydroelectric project tunnel in Sikkim, northeastern India, which claimed the lives of ten people, authorities confirmed. The incident occurred on Monday at the state-owned National Hydroelectric Power Corporation Ltd’s (NHPC) facility on the Teesta river in the village of Samardung, according to district official Subash Ghimirey.

Preliminary reports indicate that a sudden release of gas, suspected to be methane trapped in the tunnel’s rock formations, triggered the blast. This explosion released dense fumes and toxic gases, complicating rescue operations. NHPC officials stated that 25 project workers and officials were trapped inside the tunnel, a group that includes the ten victims whose bodies have already been recovered.

Survival prospects for those still inside the tunnel are considered slim, given the hazardous conditions and difficulty rescuers face due to lingering fumes, said Rajiv Roka, a state disaster management official. Rescue teams were seen equipped with oxygen supplies, ropes, and other emergency gear as they worked at the site, according to photographs shared by the state government on social media.

Efforts to locate and extract the trapped workers are ongoing, with authorities emphasizing the challenging terrain and toxic environment as major obstacles. The NHPC and local disaster response units continue coordinating rescue operations amid mounting concerns for the remaining personnel inside the tunnel. No further details have yet been released regarding the precise cause of the gas accumulation or the timeline for completing the rescue.