The incident occurred on Monday in the Himalayan state of Sikkim, where workers were building a tunnel for a state hydroelectric project on the Teesta River.
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“We believe that approximately 25-27 people are trapped,” Rajivas Roka, director of Sikkim State Disaster Management Authority, told AFP news agency. “The bodies of nine people have been found.”
The collapse was most likely caused by an explosion, the cause of which has not yet been determined.
Heavy monsoon rains have been lashing the region in recent days.
R. Roka stated that officials “are not sure what caused the explosion, as it occurred deep inside the tunnel,” adding that the explosion “was most likely natural.”
Toxic methane gas leaking from underground rock formations hampered rescue efforts, allowing only teams with oxygen equipment to enter, officials said.
“Active rescue operations are underway, but the problem is that there is a lot of gas there,” said R. Roka.
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He added that a specialized team trained to work in mining accidents had flown in to assist the rescuers.
Accidents at large infrastructure construction sites in India are common, but environmentalists say that overly intensive development projects in fragile Himalayan ecosystems have further increased the number of accidents.
In 2023, 41 workers were rescued after 17 days spent trapped under a collapsed Himalayan road tunnel in the northern state of Uttarakhand.
