The power grid is under pressure on Monday after one of Koeberg's units – which produces 900 MW – has been taken out of service, Eskom said.

"Unit one is out of service because of a technical fault," Eskom spokesperson Khulu Phasiwe said.

"The power system is relatively stable, but the grid will be under pressure later today because we have lost 900 MW from that unit."

The unit went down on Sunday.

"We have decided to take out unit one so that we can inspect it and see what is the fault on that transformer. This morning we are going to get feedback from technicians on a way forward."

The same unit was due to undergo maintenance next Monday.

"The technicians will inform us whether they will bring forward the scheduled maintenance, or whether the fault on the transformer is minor and can be fixed to bring it back to normal."