According to a senior police official in Eluru here, the five persons, aged between 21 and 25, were cleaning a tank filled with chemicals, used for shrimp processing, when they inhaled the gas, and died.
The poisonous gas was suspected to be ammonia, police said.
The tank is located over 100 meters away from Anand Aqua Food Processing unit at Nallavari Cheruvu under Mogalturu.
The deceased belonged to villages in the vicinity of the plant, police said.
Also, Deputy Chief Minister (Home) N China Rajappa spoke to district Superintendent of Police Bhaskar Bhushan and directed senior police officials to rush to the spot and submit a report.
YSR Congress president Y S Jaganmohan Reddy expressed shock and grief over the incident. He conveyed his condolences to the bereaved families.