A 60-year-old woman, her daughter and her granddaughter died in Pudunagar here on Tuesday after inhaling poisonous gas that had filled a toilet of their house, police said. The gas was emanating from the underground drainage system.

Senthamarai collapsed after entering the toilet. Her daughter Kamatchi who rushed to pick her up also fell victim to the gas, they said.

Police said seeing them unconscious, Senthamarai's granddaughter Baghyalakshmi also entered the toilet. They were rushed to a hospital by neighbours, police said and added that doctors declared they had died after inhaling poisonous gas.

Police and fire service personnel rushed to the spot and asked residents of the neighbourhood to leave their homes as the source of the gas was the underground drainage system.

Chief Minister N Rangasamy announced a Rs 20 lakh compensation for the next of kin of the deceased and ordered an inquiry into the incident.