Embattled State-owned power utility Eskom has warned that the power system will be severely constrained for the week ahead as the return to service of generation units has been delayed.

"Eskom wishes to inform the public that the power system will be severely constrained this coming week due to the unavailability of eight generation units due to breakdowns or delays in the maintenance programme," Eskom said in a statement late on Sunday afternoon.

While some of the units would be returned to service on Sunday evening and on Monday, the system was expected to remain severely constrained for the rest of the week, the statement said.

The return to service of a generation unit each at the Duvha and Medupi power stations had been delayed. Generation units at Tutuka, Majuba, Komati, Kendal, and two units at Hendrina had been shut down.

Eskom again reminded members of the public that the "aged generation infrastructure is unreliable and volatile". While Eskom teams were working hard to return as many as possible of these generation units to service, any further deterioration in the generation performance may tip the country into load shedding.

"We urge the people of South Africa to help reduce electricity usage in order to assist Eskom to keep the lights on," the utility said.