The blast at a pharma unit on Monday was the third industrial accident in two months in Visakhapatnam.
People living in a radius greater than 0.6 km from the plant would have got 30-40 minutes to evacuate the premises if an alarm had sounded within five minutes, a report says.
Authorities doubled the evacuation area around the factory to a 5 kilometre radius on Friday.
A spokesperson for the company said it was not possible to maintain the right temperature in its storage tanks during lockdown.
The Andhra Pradesh government has announced an ex-gratia of Rs 1 crore for families of the deceased.
According to Visakhapatnam Collector Vinay Chand, the gas leakage occurred after a fire broke out at the plant where workers were preparing to restart it.
The West Vizag ACP told HuffPost India that at least 70 people were in critical condition in different hospitals while DGP said 20 people were on ventilators.