The explosion occurred at 7.45am on Monday at the Natref refinery in the Free State, according to South Africa’s energy and chemical company Sasol, which operates the refinery with French oil company Total.
Emergency services spokesman Russel Meiring said 10 refinery employees suffered minor injuries in the blast; one was moderately injured.
All were taken to a medical centre.
Sasol said all personnel were evacuated from the area.
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Meiring was unable to say what had caused the explosion and whether it caused a fire.