Eskom has requested the public to reduce electricity usage as the system is severely constrained following unplanned breakdowns.
"Eskom appeals to the public to reduce electricity consumption as the generation system is severely constrained," the power utility said in a statement on Tuesday afternoon.
"We have unexpectedly lost four large units to unplanned breakdowns, while the return to service of another two generation units have been delayed.
"The breakdowns happened to a unit a Kendal, Majuba and Lethabo power stations. Furthermore, a unit at Duduva and Tutuka power stations has not returned to service as expected.
"A further Kendal unit was taken off due to technical difficulties and to address emissions.
"Eskom has 31 000MW available total capacity to meet demand tonight. While we expect some units to return to service soon, this situation may persist until the weekend.
"We urge the public the reduce consumption by switching off non-essential appliances in order to mainatian the integrity of the system."