Ten workers were killed, and 15 others remain trapped inside a tunnel under construction in the state of Sikkim, northeastern India, following an explosion believed to have been caused by methane gas accumulation, which led to a landslide that blocked the tunnel entrance and trapped workers inside.

Indian authorities said that 25 workers, including employees of the National Hydropower Corporation, were inside the tunnel at the time of the incident, before the explosion and landslide cut off the exit route.

The local administration confirmed that 10 workers were killed, while rescue teams continue their efforts to reach and extract the 15 trapped workers amid extremely difficult field conditions.

According to preliminary information, the explosion occurred at an estimated depth of 1.5 kilometers inside the tunnel during ventilation work believed to have ignited or exploded accumulated methane gas at the site.

The explosion caused a collapse of part of the soil and rocks at the tunnel entrance, blocking the exit route and complicating access to the trapped workers.

Authorities are working to determine the exact causes of the incident, while rescue teams continue to assess gas levels inside the tunnel and verify the safety of routes that can be used to reach the workers.

Rescue teams are continuing search operations for the second consecutive day inside the tunnel belonging to the 'Teesta Stage VI' hydropower project in Namchi district, Sikkim state.

Rescue operations face major difficulties due to soil and rock collapse, narrow spaces inside the tunnel, as well as risks associated with the possible presence of flammable gases, which requires rescue teams to move with extreme caution to avoid new collapses or explosions.

The incident comes to highlight again the risks associated with tunnel and hydropower projects, especially in mountainous areas with complex terrain, where excavation work requires strict procedures for ventilation, gas monitoring, and soil and rock reinforcement.

Sikkim state, located in the Himalayan region, is one of the rugged mountainous areas of India and hosts several hydropower projects, but its geographical nature makes rescue and incident response operations more difficult, especially when collapses occur inside tunnels and underground facilities.