South Africa's electricity utility Eskom said on Thursday it would implement rotational powercuts from 8am to 10pm  due to an increase in breakdowns of its generation units, warning that the blackouts could continue into the weekend.

"The delay of the return to service of two units at Duvha and Tutuka and the breakdowns of four units at Kriel, Tutuka and Kendal have resulted in the need for load-shedding today," it said in a statement.

"These units removed more than 2 000 MW of capacity from the system. Eskom is working hard to return as many of these generation units to service as possible."

It said this would necessitate "Stage 2" load-shedding, entailing the suppression of 2 000 megawatts of demand to avoid tripping the national grid.

"There is a high possibility that Stage 2 load-shedding may be escalated to Stage 3 for the evening peak. This constrained supply situation may persist throughout the weekend," Eskom warned.

The company, which supplies about 95 percent of South Africa's electricity, most of it coal-fired, has been forced to apply load-shedding on and off in recent years due to breakdowns largely attributed to years of inadequate maintenance.

"Eskom wishes to assure the public that implementing load-shedding is the last resort, in order to protect the national grid," it said on Thursday.

Eskom is one of several State-owned companies embroiled in the so-called "State capture" corruption scandal in which the wealthy Gupta family allegedly conspired with politicians in former president Jacob Zuma's administration to influence decision-making in order to advance their own interests.