Though the exact reason behind the accident is yet to be ascertained, it is suspected that the labourers died of asphyxiation while removing the centring of the septic tank, which had a very narrow opening.

Officials said two labourers had entered the septic tank to take out the wooden planks used for roof centering. The two victims reportedly fell unconscious as soon as they entered. When the third labourer called out to them, they did not respond, following which he also entered the tank and fell unconscious.

The three were rescued in a critical condition by fire services personnel and rushed to a local hospital where they were declared dead on arrival.

“It is likely that the septic tank was full of carbon dioxide and they all fell unconscious after inhaling the gas,” a fire official said.