Eleven people, including three children, died allegedly after inhaling toxic gas in a thickly populated neighbourhood in Ludhiana on Sunday, with high levels of hydrogen sulphide detected in the air and authorities suspecting it was emanating from a sewer.

A few people who had come to a local grocery store to buy milk in the morning fainted. Four people died on the spot while the others were rushed to hospital.

Among the dead were three members of the family that owned the store and five from another.

Four more people are undergoing treatment at a hospital, officials said. A cat was also found dead.

The officials said the area had been sealed and residents evacuated. A National Disaster Response Force (NDRF) team was at the spot.

A magisterial inquiry has been ordered while the Ludhiana police have registered an FIR against unknown persons.

Air quality sensors used by the NDRF team had detected high levels of hydrogen sulphide gas, according to an official release from the district administration.

Officials said they suspected that the poisonous gas was released after some chemical was disposed of in the sewerage.

Giaspura, where the gas leak occurred, is a thickly populated area with a migrant population. Several industrial and residential buildings are located there.

The victims hailed from Uttar Pradesh and Bihar.

Punjab health minister Balbir Singh visited the affected area and the civil hospital in Ludhiana. He said that exemplary action would be taken against those responsible for the tragedy.