Eskom said on Tuesday that the country's electricity system was "severely constrained" and it was relying on emergency resources - diesel and pumped water storage - to keep the lights on.

Since the weekend plant performance had "deteriorated with unplanned breakdowns" taking 12,500MW out of the system. That figure was reduced to 11,500 MW by 10am on Tuesday.

The power utility said several units were expected to return to service on Tuesday and Wednesday and, with its current diesel reserves, the probability of load-shedding remained low for the rest of the week.

The system would be constrained until at least Thursday.

Eskom has a total capacity in the region of 46,577MW.

The recent breakdowns have necessitated the use of open cycle gas turbines running on diesel, which is costly, and pumped water storage to bolster supply.

“We remind customers that any unexpected shift, such as additional unplanned breakdowns or the unavailability of diesel or pumped water storage reserves, could result in load-shedding at short notice," Eskom said in a statement on Tuesday.

 “As communicated in the Summer Plan on September 4 2019, unplanned breakdowns above 9,500MW require the use of emergency resources at a high rate [diesel and pumped water storage generators] and they increase the probability of load-shedding if the supply constraints are sustained for a long duration.”