Stage one rolling power cuts will be implemented on Tuesday morning, power utility Eskom said.

"The system is severely constrained. Therefore we have had to implement stage one load shedding from 10am to 10pm," spokesperson Khulu Phasiwe said.

Stage one allows for up to 1 000 MW of the national load to be cut, stage two for up to 2000MW, and stage three for up to 4 000 MW.

Phasiwe said the power cuts could end earlier if consumers used electricity sparingly.

The power grid was under pressure on Monday after one of Koeberg's units – which produces 900 MW – was taken out of service because of a technical fault.

Phasiwe said the unit was still down on Tuesday.

"We are trying to sync it into service. It will take a few days but it should be online soon."