Inspectors from the Department of Labour have shut down operations at the Sasol plant in Secunda in Mpumalanga following an explosion that killed six workers and injured several others.
Authorities have confirmed that at least 16 other people are in a critical condition.
It is not clear what caused the explosion at the Sasol's Polymers' ethylene plant.
Labour department spokesperson Monwabisi McClean confirmed that inspectors had issued the company with a prohibition order calling for the immediate suspension of work and services until the cause had been identified.
Police and government inspectors are currently combing the plant for clues and securing the safety of officials there while emergency services are attending to the injured and affected by the blast.