Eskom on Monday began power cuts due to problems at its power stations.
"The power system is severely constrained today due to unforeseen technical problems at power stations," Eskom said in a statement.
"As a result Eskom has had to go into stage one load shedding as of 11am. This will continue until 10pm this evening."
The utility appealed to people to switch off geysers, air conditioners, pool pumps, and all non-essential appliances.
It asked shopping centres and office blocks to switch off non-essential lights and put photocopy machines and computers on standby after hours.
"Eskom will provide regular updates on the status of the power system through all media platforms," it said.
Stage one allows for up to 1000MW of the national load to be shed, stage two for up to 2000MW, and stage three for up to 4000MW.
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