At least nine workers were killed and fifteen others remained trapped after a tunnel under construction for a hydropower project collapsed in Sikkim, northeastern India. The incident occurred on Monday near the Teesta River, according to officials who briefed reporters on Tuesday. Rajib Roka, director of the Sikkim State Disaster Management Authority, said that between 25 and 27 people were initially trapped, and nine bodies have been recovered so far.

Preliminary reports suggest that an explosion deep inside the tunnel may have triggered the collapse, though the exact cause remains uncertain. The region has experienced continuous heavy monsoon rains in recent days, which may have contributed to the disaster. Toxic methane gas released from underground rock layers has complicated rescue efforts, allowing only teams equipped with oxygen gear to enter the tunnel.

Authorities have flown in a specialized rescue team trained for mining accidents to assist in the operation. Environmental experts have warned that rapid infrastructure development in the fragile Himalayan region increases the risk of such disasters.