After some its generating units failed over the weekend, South Africa's power supply was running dangerously low by Wednesday morning.

Eskom is now battling an electricity shortfall of 12 000MW due to these breakdowns and unplanned maintenance.

In a statement issued on Wednesday morning, Eskom said that while some of these units are back online, along with others that have been down due to scheduled maintenance, they are not generating sufficient electricity to meet the current demand. 

Any unplanned outages above 9 500MW means Eskom has to resort to emergency power generation: open cycle gas turbines and pumped storage hydro electrical plants. These are very expensive ways of generating power, particularly gas turbines as they require large quantities of diesel. They can only be used for short periods before diesel and water reserves start running out.

"Eskom has since Monday increased its usage of its pumped storage and diesel generators to keep the lights on. The extensive use has led to a decline in pumped storage water and diesel levels and a concerted effort is being made to replenish these reserves," the utility said in on Wednesday morning.

Its emergency response command centre is now trying to supplement diesel to "avoid and/or if unavoidable, minimise load-shedding".

"The probability of load-shedding remains and any shift of the system could result in load-shedding at short notice," Eskom said.

It advised customers to check their load-shedding schedules.

An update on the power situation will be provided later on Wednesday.

Eskom urged customers to use power sparingly, by setting air conditioners' average temperature at 23 degrees and switching off geysers.

Last month, South Africans suffered five days of load-shedding after outages at five units. Eskom also resorted to emergency power generation, but when  its diesel stocks started running low, it was forced to shed power.