At least six workers were charred to death and 12 others grievously injured when a reactor in a chemical factory at Akkireddigudem village in the new Eluru district of Andhra Pradesh, blew up and caused a fire in the wee hours of Thursday.

Eluru district Collector V Prasanna Venkatesh, who visited the accident spot, ordered immediate shutdown of the Porus Laboratories unit pending a detailed investigation.

"We are investigating what led to the accident. Did high pressure cause the reactor to blow up, whether hazardous chemicals were being used we will probe all such aspects. We are also investigating if any rules were violated in the operation of the plant," Venkatesh told reporters.

State Chief Secretary Sameer Sharma spoke to the Eluru district Collector over phone from New Delhi and enquired about the incident. The Chief Secretary directed the Collector to conduct a thorough inquiry into the mishap and submit a report.

State Disaster Response and Fire Services personnel, as well as NDRF men, carried out the rescue and relief operations. The fire was doused in a couple of hours and the situation remained normal.

Residents of Akkireddigudem staged a protest outside the plant, demanding that it be relocated from the village forthwith. The villagers alleged that the plant caused water and air pollution, making their life miserable.

"Even crops are not growing properly because of the pollution and we have been demanding for long that the plant be shifted from here," the protesting villagers said.

Hyderabad-based Porus Laboratories, which is into manufacturing of pharmaceutical intermediates and specialty chemicals, has five units in different locations in Andhra Pradesh and Telangana.

More than 50 workers were at work in the night shift on Wednesday when the mishap occurred in unit-4, killing at least five on the spot. Another worker succumbed while being taken to hospital in Nuzividu.

Four of the deceased were said to be natives of Bihar.

After first aid in Nuzividu hospital, the 12 injured workers, some of whom had sustained 80 per cent burns, were rushed to the Government General Hospital in Vijayawada, a senior police official said.

Nuzividu MLA Meka Pratap Appa Rao, who visited the Porus unit, said it was an accident.

While the state government announced a compensation of Rs 25 lakh each to the kin of the deceased, the factory management too would pay an equal amount, the MLA said.

The state government also announced Rs 5 lakh each to the seriously injured and Rs 2 lakh each to the injured persons.

Andhra Pradesh Governor Biswa Bhusan Harichandan, Chief Minister Y S Jagan Mohan Reddy, Leader of Opposition N Chandrababu Naidu, Jana Sena chief K Pawan Kalyan, Pradesh Congress president Sake Sailajanath and others expressed shock and grief over the tragedy.