Bhubaneswar: Three workers suffocated to death while centering the roof of a septic tank in Sambalpur district of the Indian state of Odisha on Saturday. One of them is currently being treated in hospital where his condition is considered critical, officials said.

Officials said the workers were busy centering a septic tank next to a toilet under construction in Pukuda village near Jamankria police station.

The cistern was built about four months ago, but centering had not yet been completed and was scheduled for Saturday, officials said.

The workers lost consciousness due to suffocation after entering the septic tank, officials said, adding that others present immediately pulled them out and took them to a nearby hospital, where doctors declared three of them dead.

The dead were identified as Srikant Munda, Bharat Rana and Basant Dehury. Another worker, Siddharth Mund, who fell unconscious, was taken to the district hospital.

According to doctors at the hospital, the suffocation could be due to toxic gases in the tank. These gases may include methane, hydrogen sulfide, ammonia, carbon dioxide, carbon monoxide, sulfur dioxide and nitrogen dioxide.