South Africa's state-owned utility on Thursday declared an energy emergency, warning of possible blackouts after coal shortages and technical problems seriously reduced generation capacity.
"Eskom has declared an emergency at 06:00 (0400 GMT) this morning," it said in a statement.
Incessant and heavy rains over the past week left coal too wet to use at its coal fired generation plants.
"The power system is very tight," it said.
It has has asked major industrial customers to reduce usage by at least 10 percent, to prevent load shedding.
The risk of outages "has increased significantly due to the heavy rains over the last few days and an increase in technical problems experienced at some of Eskom's power stations."
South Africa last suffered widespread and rolling blackouts in 2008 when factories and mines were forced to shutter, costing the economy billions of dollars.
Eskom is battling to keep Africa's largest economy powered up as it races to construct new plants amid rising demand.
This is the fourth energy emergency declared in just as many months and "it's the worst one so far," according to an Eskom official who asked not to be named.
The company supplies around 95 percent of the country's electricity.