South Africa's state-owned electricity company Eskom has stopped supplying power to neighbouring countries because of acute domestic shortages.
South Africans are not used to power cuts
Zimbabwe and Mozambique are thought to be the worst affected countries.
A BBC correspondent says the recent daily power cuts have caused chaos and are threatening to have a major impact on South Africa's economy.
On Friday, enraged commuters set fire to trains in Pretoria after power cuts caused two-hour train delays.
The BBC's Peter Biles in Johannesburg says many small businesses are being crippled by the blackouts.
Economists are warning that the country's target of 6% economic growth by 2010 - when South Africa will host the football World Cup - is fast becoming a pipedream.
President Thabo Mbeki on Sunday met Eskom's executives to discuss the power shortages.
Mr Mbeki last month admitted the government had been wrong to refuse Eskom's request for more investment in power generation several years ago, reports the AFP news agency.
"We were wrong. Eskom was right," Mr Mbeki said.
The governing African National Congress has now recommended the urgent development of a national response plan, to keep the electricity flowing.
Zimbabwe was hit by a black-out on Saturday night, although power was later restored.
It is not clear if this was linked to the Eskom decision.
State radio has blamed the problem on an unspecified breakdown.
Zimbabwe is believed to import about 40% of its electricity and has had trouble paying its bills because of its lack of foreign currency.