Explosion in Indian hydropower project tunnel leaves 11 dead and 14 missing

At least 27 people were trapped, including some who entered the tunnel to help with rescue efforts after the blast, while two workers escaped, Tamang said.

The blast ripped through the tunnel at Samardung village, about 40 kilometers (25 miles) from the state capital, Gangtok, where multiple workers were carrying out construction work on the 500-megawatt Teesta hydroelectric project, civil official Anupama Tamling said.

Survivors told authorities they heard a loud explosion before debris came crashing through the tunnel, trapping dozens inside, Tamling said.

Officials had recovered 11 bodies on Tuesday while rescue teams including the National Disaster Response Force (NDRF) raced to reach at least 14 people who remained trapped inside the tunnel, where toxic gases and hazardous conditions have hampered operations.

“We found toxic gases such as methane, carbon monoxide and hydrogen sulfide inside the tunnel,” NDRF official Nitin Kumar said at the scene, adding that rescuers were using breathing equipment as they searched in the for survivors in the dangerous air conditions.

As news of the accident spread, six officials from the state-owned National Hydroelectric Power Corporation (NHPC), which is building the project, entered the tunnel to assist in rescue efforts but became trapped themselves, officials said.

Construction accidents are not uncommon in India, where rapid infrastructure growth often collides with fragile geology, construction lapses, extreme weather and safety standards.

In the Himalayan region, fragile mountains, seismic activity and unpredictable underground conditions make tunnel projects especially risky. An explosion inside a coal mine in neighboring Meghalaya state in February killed at least 18 workers. In 2023, a tunnel section in northern Uttarakhand state collapsed, trapping 41 workers for 17 days before they were rescued.

Experts say the Teesta River basin, where the hydropower project is being built, lies in a seismically active region marked by young, fragile rock formations riddled with fractures and underground pockets that can trap ancient gases.

Dr. Devesh Walia, a geology professor at North-Eastern Hill University in Meghalaya, said the area contains relatively young rock formations, some associated with coal-bearing strata.

“It is quite possible that methane along with other gases accumulated underground and may have triggered an explosion,” he said.