South African electricity public utility, Eskom, on Monday confirmed that the Medupi power station experienced an explosion on the Unit 4 generator.
According to local publication Times Live, the incident occurred at about 10.50pm on Sunday, and is suspected to have resulted in Unit 5 tripping.
The utility said that no injuries have been reported and all employees and contractors have been accounted for.
Emergency services attended to seven colleagues requiring treatment for shock.
Times Live reported that all work on the unit was suspended with immediate effect, including the suspension of all permits to work on the plant until further notice.