The "Stage 6" power cuts mean six to eight hours a day without power for most South Africans and require up to 6,000 megawatts (MW) of capacity to be shed from the national grid.
They are a major source of public frustration with the governing African National Congress party, whose support among voters is sliding, and a brake on economic growth in Africa's most industrialised nation.
Eskom has a nominal generation capacity of roughly 46,000 MW, but on Wednesday more than 23,000 MW of that was offline because of breakdowns or planned repairs.
Eskom said in a statement that 11 of its generators had suffered breakdowns since Tuesday morning.
The beleaguered utility supplies the vast majority of South Africa's electricity, relying mainly on an ageing fleet of coal-fired power stations that are unreliable and prone to faults.
The country witnessed more than 200 days of power cuts in 2022, the most in a calendar year, and the situation could get even worse in 2023.
Since taking office in 2018, South African President Cyril Ramaphosa has been trying to reform debt-laden Eskom to make it more efficient but progress has been slow.
Eskom CEO André de Ruyter submitted his resignation last month, making him the 11th boss to leave the company in just over a decade.
Police are investigating whether an attempt was made to poison de Ruyter, who has pursued a clampdown on corruption and organised criminal behaviour, including sabotage of infrastructure, at Eskom plants.
(Reporting by Bhargav Acharya; Editing by Alexander Winning and Bernadette Baum)
