Johannesburg - Nationwide power cuts across South Africa of up to 4 000 megawatts will last indefinitely, state power firm Eskom said on Thursday, as repairs take longer than anticipated.

Eskom had said on Wednesday the outages would last only until Friday.

The latest load shedding was triggered by breakdowns this week at a score of generating units, including at Koeberg nuclear plant in Cape Town.

"Due to a shortage of generation capacity resulting from unplanned breakdowns, Eskom will continue implementing Stage 4 loadshedding until further notice. We expect that load shedding, at various stages, may continue into the weekend," Eskom said in a statement.

"The pump fault on Koeberg Unit 1 is being fixed, and it is envisaged that the unit will be back in service at the weekend. In the meantime, we continue utilising emergency generation reserves, including diesel, to supplement supply," Eskom said.