NEW DELHI, July 22, 2026 (BSS/AFP) - The death toll from a tunnel collapse at an under-construction hydroelectric project in India's remote northeast has risen to at least 20, officials said Wednesday.

The incident occurred on Monday in Namchi district in the Himalayan state of Sikkim, where workers were constructing a tunnel for a state-run hydropower project on the Teesta river.

"Out of the 25 who were trapped, 13 bodies have been recovered so far," Rajiv Roka, director of the Sikkim State Disaster Management Authority, told AFP.

"The rescuers have also seen seven to eight more bodies inside but they have not been able to retrieve them so far."

Water-logging and methane gas leaking from underground rock formations at the site were hampering rescue efforts, officials said.

"There was a collection of water... it was around two-and-a-half feet (0.76 metres) so it's been difficult to retrieve the bodies," Roka said.

"Looking at the condition, I don't think there could be any survivors."

The region has seen torrential monsoon rains in recent days.

The collapse was triggered by an "explosive release of suspected methane gas trapped/embedded in the rocks, resulting in the generation of dense smoke and toxic gases", the National Hydroelectric Power Corporation (NHPC) said in a statement.

"A detailed investigation will be conducted to ascertain the cause of the incident," the company added.

Accidents on large infrastructure construction sites are common in India, but environmental experts say excessive development projects have led to more disasters in the fragile Himalayan areas.

In 2023, 41 workers were rescued after 17 days of being trapped under a Himalayan road tunnel that had collapsed in northern Uttarakhand state.