GUWAHATI — A methane gas leak triggered the explosion and collapse inside an under-construction hydropower tunnel in India's northeastern state of Sikkim that has killed 12 people, state authorities said on Wednesday, as rescue teams continued searching for 13 others believed to be trapped.
Sikkim Chief Minister Prem Singh Tamang said preliminary findings indicated that a sudden buildup and explosion of methane gas, rather than a landslide, caused Monday's disaster at the NHPC Teesta Stage VI Hydroelectric Project in Samardung, Namchi district. He announced a high-level inquiry to establish the exact sequence of events and determine responsibility.
The blast occurred inside the project's head race tunnel while workers were carrying out construction activities. Authorities said the explosion filled the tunnel with toxic gases and debris, complicating rescue operations and limiting the time emergency personnel could remain underground.
Officials said 12 bodies have been recovered while 13 people remain unaccounted for. Rescue efforts involving the National Disaster Response Force, State Disaster Response Force, police and other agencies entered a third day on Wednesday but were slowed by hazardous concentrations of methane and other gases, low oxygen levels and water accumulation inside the tunnel.
According to NHPC, the state-owned power company developing the project, the incident followed a sudden burst of suspected methane gas trapped within surrounding rock formations, leading to an explosion that generated dense fumes and toxic gases inside the tunnel. The company said it was cooperating fully with rescue operations and the official investigation.
Administrative officials said specialized breathing equipment and protective gear were being used because rescuers could work inside the tunnel only for short periods before withdrawing due to dangerous air conditions. Authorities have not released the identities of all those killed or missing.
The Teesta Stage VI project is located in the Himalayan region, where complex geology, fractured rock formations and seismic activity pose significant engineering challenges for large infrastructure works. Experts have said underground pockets of naturally occurring gases can present additional risks during tunneling operations.
The Sikkim government said the inquiry would examine the cause of the explosion, safety procedures and emergency response measures. Officials said search operations would continue until all missing workers were accounted for.
