The "Stage 2" power cuts require up to 2,000 megawatts (MW) of capacity to be shed from the national grid.

"Whilst still recovering four units at Tutuka, which had experienced conveyor belt failures, the fleet suffered a cluster of boiler tube leaks within a short period of time," Eskom said in a statement.

"Emergency reserves have been further depleted today due to breakdowns of a generating unit each at Kusile, Komati and Hendrina power stations," it added.

Eskom said total breakdowns amounted to around 14,760 MW of capacity while another 5,280 MW was offline due to planned maintenance. Its nominal capacity is around 46,470 MW.

Eskom implemented scheduled power cuts on Thursday for the first time since July. On Thursday it said it planned to implement outages from Thursday evening to Friday morning and Friday evening until Saturday morning but said they could be extended if emergency reserves could not be replenished.

(Reporting by Alexander Winning in Johannesburg; Editing by Matthew Lewis)