Various parts of the country experienced blackouts on Thursday after Eskom declared an emergency.
Seven days of heavy rain had left coal stocks wet and staggered power cuts were introduced throughout the country, the power utility's spokesperson Andrew Etzinger said.
"We have asked our large industrial customers to reduce their consumption by 10% but it appears this will not be enough."
Eskom appealed to the public to reduce their electricity usage to help ease the demand for power.
Hospitals and clinics were urged by the Democratic Nursing Organisation of South Africa (Denosa) to ensure their generators were working properly during the power cuts period.
"It is a fact that not all health facilities put the necessary measures in place," said Denosa spokesperson Sibongiseni Delihlazo.
"Previous experience teaches that during unannounced power outages, some hospitals are often found with their proverbial pants down as generators fail to kick in."
On Thursday, flights were delayed at the OR Tambo International Airport, outside Johannesburg, after a power cut.
Airport spokesperson Unathi Batyashe-Fillis said while essential services operated on back-up power, backlog was experienced because some services had to be facilitated manually.
In the eastern Free State, citizens who were not paying for electricity were told their power would be cut.
Local electricity management company Rural Maintenance said some 40% of electricity users in the region's Maluti-a-Phofung Local Municipality were not paying for their power supply.
"These customers were therefore directly responsible, with all the other such users, of Eskom having to load-shed paying citizens," its chief executive Chris Bosch said.
He said it was going to help Eskom decrease the load on its supply system by disconnecting all non-paying users.
The Maluti-a-Phofung municipality includes Phuthaditjhaba, Harrismith, and Kestell.
In Tshwane, power was cut for about two hours on Thursday.
The areas affected included Waterkloof, Pumulani, Koedoespoort, Tonnel, Mayville, Highlands, Soshanguve, Montana, Rosslyn, and Pretoria North.
City spokesperson Selby Bokaba said rotational power cuts were implemented following an instruction from Eskom.
"The objective of rotational load shedding on a two-hourly basis is to help ease the demand for power."
In Johannesburg, power cuts were experienced since 8am.
City spokesperson Hloni Motloung said the affected areas included Hillbrow, Berea, Houghton, Parktown, Rosebank, Hyde Park, Inanda, Alexandra, Rembrandt Park, Sunningdale, and Lombardy.
The City of Cape Town initiated "stage three" power cuts.
"Stage three is the highest level of load shedding possible," said spokesperson Neil Ballantyne.
A number of suburbs in Port Elizabeth were also without electricity until midday, the Nelson Mandela Bay Municipality said.
The areas affected included New Brighton, Seaview, Walker Drive, Brickmakerskloof, Vuyisile Mini Square, Newton Park, and Linton Grange. – Sapa