Four people were injured when a chemical factory exploded in Boksburg, Ekurhuleni, on Thursday afternoon.
One person was in a critical condition due to facial, neck and inhalation burns, while the other three were in a serious but stable condition.
The three were taken to the Tambo Memorial and Sunshine hospitals for smoke inhalation and superficial burns.
READ: 4 seriously injured in chemical explosion at Boksburg factory
City of Ekurhuleni Disaster and Emergency Management Services spokesperson William Ntladi said the explosion could be seen and heard from a distance.
"Some of the 210-litre containers from within the workshop were ejected through the roof," he said.
The cause of the fire has not yet been determined, although it is thought that it may have been caused by a chemical reaction.