Electricity company Eskom said it did not expect to implement rotational load-shedding on Thursday, but the system remained extremely constrained and vulnerable.

"There is sufficient diesel for our open cycle gas turbines and water at the pumped storage schemes to supplement the shortage of capacity, if required," the state-owned utility said in a statement.

"A concerted collective effort to reduce demand can help to lessen the level of load-shedding. And as such, we strongly urge customers to assist by helping to reduce demand by using electricity sparingly."

Because of years of inadequate maintenance, Eskom's generating units are prone to breakdowns, forcing the company to implement rolling blackouts several times this year to avoid tripping the national grid.