South African power utility, Eskom, on Tuesday announced Stage 4 load-shedding from 14:00 after Koeberg Power Station's unit 1 tripped.
"The unit has been disconnected from the grid due to a fault on the turbine side, however, the nuclear reactor remains safe. The teams are investigating the root cause of the fault and will advise on the remedy as soon as it is established," Eskom said.
"The loss of approximately 930MW unit puts further strain on the generation fleet, necessitating an increase in the stage of load-shedding. As the ageing fleet is currently constrained, unpredictable and vulnerable, we advise South Africans that the stage of load-shedding may change at short notice should there be any unexpected change in the generation system performance."
The power utility said that demand in electricity had also increased since January.
It urged South Africans to cooperate in managing the country's electricity consumption to help minimise load-shedding.