South Africa's electricity system remains extremely constrained and vulnerable as generating plants perform at very low levels of reliability, with a probability of rotational blackouts being implemented if there is any unexpected deterioration, power company Eskom said on Monday.

Eskom said it had made good progress over the weekend to replenish diesel for its open cycle gas turbines and to increase water levels at pumped storage schemes.

Years of failure to adequately maintain its infrastructure have left Eskom's generating units vulnerable to breakdowns, forcing the cash-strapped State utility to implement rolling powercuts several times this year to avoid tripping the national grid.

Eskom, which has not implemented load-shedding since Friday morning, said it did not expect to do so on Monday as unplanned breakdowns remained marginally below 9 500 MW.

"But the probability of load-shedding remains if there is any unexpected shift on the system," it cautioned, referring to possible additional unplanned breakdowns or the unavailability of diesel for open cycle gas turbines or water levels at pumped storage schemes.

It said its Emergency Response Command Centre continued to monitor the system on the hour, with the generating plant performance remaining unpredictable.