Eskom said the power cuts, called "load-shedding" locally, would last from 10 p.m. (2000 GMT) until 8 a.m. (0600 GMT) on Sunday.

The cash-strapped utility has been battling to keep the lights on, despite low electricity demand over the Christmas and New Year public holidays. It last implemented power cuts in mid-December.

As of 0430 GMT on Saturday, almost 16,000 MW of Eskom's 44,000 MW nominal generating capacity was offline because of plant breakdowns.

Eskom executives have blamed repeated faults at the company's coal-fired power stations on a lack of critical mid-life maintenance at older stations, and design flaws on the mammoth Medupi and Kusile projects.

Eskom said the overnight power cuts would help it replenish water levels at its pumped storage facilities, and diesel stocks at its open-cycle gas turbines, to put it in a better position for next week, when many people will return to work.

It added that a number of generating units were being brought back online after repairs and maintenance.

(Reporting by Alexander Winning; Editing by Kevin Liffey)