The risk of power cuts was high on Wednesday after two of Eskom's generators failed, the power utility said.

"Two generators failed and this is part of a number of other challenges within the systems, which have exacerbated the situation," spokesperson Khulu Phasiwe said.

"We are not saying there will be load shedding, but the risk is high between now [12:00] and 22:00. If we all work together and use electricity sparingly, we can avoid load shedding."

Engineers were trying to determine why the generators broke down and how long it would take to fix them.

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.

South Africa's power grid is under "significant pressure" at the moment as the continent's most advanced economy reboots after the festive season and the reserve margins are expected to be "very tight" next week, Eskom spokesperson Andrew Etzinger said on Wednesday.