South Africa on Monday introduced its most severe electricity rationing in nearly five years, presenting President Cyril Ramaphosa with a major political challenge just months ahead of a May general election.
The debt-laden state power utility Eskom is at the centre of the country's economic troubles and has been hit by allegations of government graft.
Ramaphosa who last week admitted that Eskom was in crisis, on Monday expressed anger at the intense power outages.
Offices, shops, factories, traffic lights and private homes were hit on Monday by "load-shedding" -- scheduled power cuts to reduce usage.
The cuts were categorised as "stage 4", the highest severity level since March 2014.
"The power system is severely constrained, which is why after a long time we have had to implement stage 4 of load shedding," Eskom spokesman Khulu Phasiwe said.
"Since this morning we have unexpectedly lost six additional generating units which have put additional strain on the system," the company said in a statement.
In a interview with state journalists at the end of the African Union summit in Addis Ababa on Monday, Ramaphosa said the sudden severe power cuts had come as a "shock".
"That is most worrying, most disturbing, and it comes as a shock," he said.
"It has shocked me and also made me quite angry that we have reached this stage of dysfunctionality," he said.
- 'Shocking, most disturbing' -
Ramaphosa last week vowed to fight mismanagement and corruption at the utility, which has 419 billion rand ($30 billion) debt, by dividing it into generation, transmission and distribution divisions.
Moody's warned Monday that financial aid to Eskom could be credit negative unless it is backed by steps to generate savings.
The country heads for polls on May 8, with the ruling ANC party keen to repair a fall in popularity in recent years.
The largest opposition party, the Democratic Alliance, blamed Eskom's woes on government graft and said it would request an urgent parliamentary debate.
"These power failures can be placed squarely at the feet of the ANC, as it has been their looting and theft of the public's money that has left us in the dark," the party said.
Political and economic commentator Daniel Silke tweeted that the outage "is the predictable end result of a toxic recipe of bad sector policy choices, ... hapless management systems, outdated desires of state control and the final killer of graft & corruption".
Eskom said the cuts would take 4,000 megawatts of demand out of the system to prevent its collapse.
It pleaded for residents and businesses to use electricity sparingly as it warned that power outages were likely to continue until April.