A devastating explosion inside an under-construction tunnel at a major hydroelectric project in India’s northeastern state of Sikkim has claimed at least 10 lives, while 17 others remain missing as rescue teams battle hazardous conditions to reach those trapped beneath the debris.
The accident occurred on Monday at Samardung village, approximately 40 kilometres from the state capital of Gangtok, where construction was underway on the 500-megawatt Teesta Hydroelectric Project near the India-China border. Authorities believe a buildup of underground gases triggered a powerful explosion that caused a section of the tunnel to collapse while workers were carrying out construction activities.
According to local officials, workers who managed to escape reported hearing a loud explosion moments before debris crashed through the tunnel, trapping dozens of people inside. As emergency operations began, six officials from the state-owned National Hydroelectric Power Corporation (NHPC), the agency responsible for constructing the project, entered the tunnel to assist in rescue efforts but also became trapped following the collapse.
Police officials confirmed that rescue teams have recovered 10 bodies so far, while 17 people are still feared trapped inside the tunnel. Emergency personnel from the National Disaster Response Force (NDRF) continue to conduct search operations despite facing extremely dangerous conditions underground.
Rescue efforts have been severely hampered by the presence of toxic gases inside the tunnel. Officials reported detecting high concentrations of methane, carbon monoxide and hydrogen sulphide, forcing rescue workers to use specialized breathing equipment while searching for survivors. The unstable structure and poor air quality have made operations slow and highly challenging.
Geologists believe naturally occurring gases trapped within the fragile Himalayan rock formations may have contributed to the explosion. Experts note that the Teesta River basin lies within a seismically active region characterized by young and fractured rock formations capable of trapping combustible gases over long periods.
Dr. Devesh Walia, a geology professor at North-Eastern Hill University in neighbouring Meghalaya, said the area’s geological composition includes coal-bearing rock formations where methane and other gases can accumulate underground. He noted that such gases may have ignited, resulting in the powerful explosion that triggered the tunnel collapse.
Construction accidents remain a recurring concern in India as the country rapidly expands its infrastructure network. Large-scale tunnel and hydropower projects in the Himalayan region face additional challenges due to unstable mountain terrain, seismic activity, unpredictable underground conditions and difficult weather.
The tragedy has drawn comparisons with the 2023 tunnel collapse in Uttarakhand, where 41 construction workers were trapped underground for 17 days before being rescued in one of India’s largest and most complex rescue operations.
Authorities have launched an investigation into the cause of the explosion while rescue teams continue their efforts to locate survivors. Officials say the priority remains reaching those still trapped, although dangerous conditions inside the tunnel continue to pose significant risks to rescue personnel.