Johannesburg, South Africa — South Africans were bracing for electricity cuts this weekend following months of reliable power supply after the national energy provider Eskom announced Friday a shortfall in generation. 

Africa's most industrialised economy has been long-beleaguered by power cuts, called loadshedding, which at crisis points have left South Africans in the dark up to 12 hours per day. 

The more than 300-day stretch of grid stability ended last week following multiple breakdowns at two major coal power plants while planned maintenance was being conducted at other sites, Energy Minister Kgosientsho Ramokgopa told a press briefing. 

"We got hit by a perfect storm," he said. 

The energy firm tried to avert power cuts by relying on diesel-fuelled turbines but reserves have now fallen short, leaving the grid vulnerable, officials said. 

Repairs are underway and one compromised unit had already returned to operation Friday, officials said. 

Still, rolling blackouts were slated to begin Friday evening and last until midnight (2200 GMT) Sunday. 

Eskom attributed the recent long stretch of stability to improved maintenance at its 13 mainly coal-fired power stations. 

"We have come to a situation where loadshedding is an extraordinary occurrence... it's an anomaly," he said, emphasising the progress from crippling blackouts in recent years. 

"The trend line is positive," he added. 

The downed stations are expected to be fully online by Tuesday, officials said.