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 0.76m 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 said in a statement.
“A detailed investigation will be conducted to ascertain the cause of the incident,” the company added.