"We apologize to the country about the impact and disruptions", Public Enterprises Minister Pravin Gordhan wrote in a statement on Thursday.
"Power cuts are having a devastating effect on households and livelihoods, investment and economic climate. This is totally unacceptable," he said.
On Wednesday, state utility Eskom said it had to ramp up power rationing to consumers, something known locally as load shedding.
This meant South Africans experienced multiple cuts, each lasting between two and four hours, on a rotational basis for up to about 11 hours a day.
The state-owned energy firm had to delay a planned maintenance outage at a nuclear power station on Thursday "to get some time to stabilize the system," a day after it announced further blackouts due to breakdowns at other plants.
Scheduled blackouts have burdened Africa's most industrialized economy for years, with Eskom failing to keep pace with demand and maintain its ageing coal power infrastructure.
The outages reached new extremes this year.
Last month, Eskom, which is struggling under a 400-billion-rand ($23.3 billion) debt - half of which the government has pledged to take on - said it had run out of funds to buy diesel.
The opposition Democratic Alliance (DA) party said the risk of a national blackout due to system failure was growing and urged the government to issue a contingency plan.