The gas escaped from a newly commissioned pipeline at paper manufacturer Sappi's Saiccor mill, near Umkomaas.
Thirty-four staff at the site, which annually produces 600,000 tonnes of elemental chlorine-free chemical cellulose, were exposed to the irritant gas. They were treated at the mill's clinic and later discharged.
Around 14 people from the local community were also exposed to the gas and have since been discharged from hospital.
General mill manager Gary Bowles said: "The mill has procedures in place to deal with eventualities of this nature on a priority basis and we were able to contain the leak promptly."
He said the mill regretted the incident and that relevant authorities would be informed and a full enquiry carried out.
Sappi said it would take further precautions to ensure no further leakages.
Staff at South African Sappi mill treated after gas leak
Staff at a pulp mill in South Africa, and up to 14 locals from the surrounding area, have had medical treatment following a sulphur dioxide gas leak.
