Johannesburg - Eskom will implement stage two black-outs from 8am on Saturday, the power utility said.

"The electricity supply system is very vulnerable due to a shortage of generation capacity as several units are currently out of service due to planned and unplanned outages," Eskom said in a statement.

"We will use the weekend to build up diesel stocks and dam water levels for open-cycle gas turbines and pumped storage schemes respectively."

The power cuts were expected to continue until 10pm on Saturday.

Eskom said it would review the electricity supply situation on Saturday evening and decide the prognosis for Sunday.

President Jacob Zuma announced during his State of the Nation Address in Parliament on Thursday that Eskom would be given R23 billion to stabilise its finances.

On Monday morning, at a breakfast meeting in Cape Town, he added that he was concerned about shortcomings in the running of the power grid and said the government wanted to establish whether this was due to negligence.

"You can't have one power station collapsing after the other because they are not serviced. Where were the people who are working there? What were they doing?"

The president described Eskom's situation as a "challenge", not a crisis.

He again blamed the scheduled blackouts, in part, on the apartheid regime's failure to expand the electricity supplier's capacity.

"If you look at energy, energy has a history in this country, it has never been enough. It was believed to be because the powers that be at the time said 'we have enough'.

"So the demand has just rocketed after 1994, and therefore undermined the capacity we have," he said.

** This story has been updated.


Reuters and Sapa