A suspected methane gas explosion triggered the collapse of an under-construction tunnel at a major hydropower project in India's northeastern Himalayan state of Sikkim, leaving at least 12 people dead while 14 others remain missing.

The explosion occurred on Monday at the Teesta Stage VI Hydroelectric Project in Samardung village, around 40 kilometers from the state capital, Gangtok, where workers were excavating the tunnel for the 500-megawatt hydropower facility.

According to local officials, survivors reported hearing a powerful explosion before sections of the tunnel collapsed, trapping dozens of workers beneath debris. State authorities believe the blast was likely caused by a buildup of methane gas trapped within underground rock formations.

The tragedy deepened after six officials from the state-owned National Hydroelectric Power Corporation (NHPC) entered the tunnel to assist in rescue efforts but also became trapped when conditions rapidly deteriorated.

Rescue operations involving the National Disaster Response Force (NDRF), local emergency services, police, and NHPC personnel have continued around the clock despite extremely dangerous conditions inside the tunnel.

Officials said high concentrations of methane, carbon monoxide, and hydrogen sulfide have made rescue efforts exceptionally hazardous, forcing emergency crews to rely on specialized breathing equipment and gas-monitoring devices while searching for survivors.

Sikkim Chief Minister Prem Singh Tamang, who visited the disaster site, said authorities are making every effort to rescue those still trapped and provide assistance to the affected families. NHPC also confirmed that senior company officials have been deployed to oversee rescue operations and coordinate with emergency agencies.

The Teesta Stage VI Hydroelectric Project is one of several large-scale hydropower developments planned along the Teesta River, which flows through the ecologically sensitive Himalayan region. The project is intended to generate 500 megawatts of electricity as part of India's efforts to expand renewable energy production.

However, experts have long warned that the Teesta River basin lies within one of the country's most geologically fragile and seismically active regions. Young rock formations, underground fractures, and trapped natural gases significantly increase the risks associated with large-scale tunneling projects.

Geologists say methane pockets embedded within the surrounding rock may have accumulated during excavation, potentially triggering the explosion that led to the collapse.

The latest disaster has once again drawn attention to safety challenges facing India's rapidly expanding infrastructure sector.

Construction accidents remain relatively common as major engineering projects increasingly extend into difficult terrain marked by unstable geology, heavy rainfall, and seismic activity.

The incident also recalls the 2023 tunnel collapse in Uttarakhand, where 41 workers were trapped underground for 17 days before being rescued in a complex, internationally watched operation. More recently, a deadly coal mine explosion in neighboring Meghalaya also highlighted the dangers posed by underground gas accumulations in the Himalayan region.

Authorities said search and rescue operations will continue until all missing workers have been accounted for, while an investigation has been launched to determine the precise cause of the explosion and assess whether safety protocols were adequately followed at the construction site. (ILKHA)