At least seven more bodies were recovered from the tunnel of an under-construction hydroelectric project in India’s northeastern state of Sikkim, the state government said Thursday, bringing the death toll from a blast to 22.

Axar.az reports, citing NBC, the incident took place Monday at state-owned National Hydroelectric Power Corp Ltd.’s project on the Teesta river in the village of Samardung.

An explosion in the tunnel, suspected to have been caused by methane trapped in or released from rocks, filled it with dense fumes and toxic gases, trapping 25 workers and officials of NHPC.

“Rescue operations remain in progress, with specialized teams working in close coordination to locate and recover the remaining victims,” the Sikkim state government said in a Facebook post.

Authorities had warned that the survival chances of those trapped were slim.