The Andhra Pradesh government has ordered a probe into the incident, the state police chief said in Amaravati.
Chief Minister YS Jaganmohan Reddy held a high-level review meeting to take stock of the situation and ordered a probe into the matter, Andhra Pradesh DGP D Gautam Sawang said.
As many as eight people were killed in the styrene gas leak incident at LG Polymers Limited plant at RR Venkatapuram near Visakhapatnam in the early hours of Thursday.
The top police officer said there was no more leakage of gas and the situation was now "stable and under control".
At least 246 persons with health complications are undergoing treatment at the King George Hospital, Visakhapatnam and 20 of them are on ventilator support, he told reporters after the meeting with the Chief Minister.
In all, over 800 persons were evacuated from RR Venkatapuram following the gas leak and most of them only needed first aid.
The Chief Minister ordered an inquiry into the gas leak incident, the DGP said.
"How the gas leaked and why the neutraliser at the plant did not prove effective in containing the leak will all be investigated. Styrene, though, is not a poisonous gas and can be fatal only if inhaled in excess quantity," Mr Sawang said.
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