LG Chem, which operates the plant, said it is cooperating with Indian authorities to help residents and employees.
"The gas leakage is now under control, but the leaked gas can cause nausea and dizziness, so we are investing every effort to ensure proper treatment is provided swiftly," LG Chem said in a statement.
The firm is looking into what caused the leak of styrene monomer gas, which is used for producing plastic.
"We are investigating the extent of damage and the exact cause of the leak and deaths," it added in a statement.
Stating that the plant operations were suspended because of coronavirus lockdown at the time of the accident, the firm said none of the LG Chem's employees have died in the accident.
LG Chem said it was seeking to ensure casualties received treatment quickly.
Company staff reportedly inspecting machines to restart the factory noticed the leak and raised an alarm.
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