Angry protesters carrying dead bodies stormed an Indian chemical plant on Saturday to demand the facility's closure after a toxic gas leak that killed 12 people days earlier.

Thursday's pre-dawn accident in the industrial port city of Visakhapatnam injured hundreds and knocked many unconscious as they tried to flee the area. State government officials had arrived to conduct a safety tour of the plant, owned by South Korea's LG Chem, when a crowd of around 300 people barged past police and security guards.

Some helped cart stretchers bearing three victims of the disaster, their feet sticking out from under the black canvas covers that otherwise shrouded the bodies. They chanted slogans demanding justice for the dead and the shutdown of the plant before they were pushed back by security.

Relatives of the dead stood nearby, many in tears, while others relieved the horror of the sudden accident. "I saw people carrying their children on their shoulders looking for water. They could not move because of the gas, I thought they were dead," said one man.

At least three children were among the dead and dozens remain in hospital. Late Thursday, an evacuation zone around the plant was widened and hundreds more people were moved to safety after fears of a new leak. Some have since been allowed to return.

Andhra Pradesh state police chief Gautam Sawang said the situation at the facility was now "under control". Authorities have started a manslaughter investigation over the leak and India's environmental tribunal has already fined the company $6.2 million as a preliminary punishment.

Police said the plant had been left idle because of India's nationwide coronavirus lockdown and suspect the leak was caused by gas left in a tanker that overheated. LG Chem confirmed that the polystyrene plant was not operating at the time of the accident, but insisted there were maintenance staff at the facility. The disaster has evoked memories of a major leak at a gas plant in the Indian city of Bhopal that killed at least 3,500 people in 1984.