One of the two Eskom generators that went offline on Wednesday has now been repaired and is producing power, the power utility said.

"The system remains vulnerable, meaning that any extra load or faults in the system may necessitate the need to implement load-shedding," spokesperson Khulu Phasiwe said.

This was however a last resort to prevent a "total collapse" of the system.

Earlier, he said the failure of the two generators was part of a number of other problems which had exacerbated the situation.

"We are not saying there will be load-shedding but the risk is high between now [noon] and 10pm. If we all work together and use electricity sparingly, we can avoid load-shedding."

On Monday, Eskom said the power grid was constrained but stable after a spike in electricity usage as people returned from holiday.

At the time, Phasiwe said Eskom was able to meet the increased demand. The risk of rolling blackouts was low to medium.

He said there had been an average daily electricity demand of 25,000MW since the start of the holidays, but this had risen to 30 000MW.

Eskom called on people to reduce power use by 10% during the day to help it conduct planned maintenance.