Eskom said there was a risk of load-shedding on Friday.
"There is a risk, yes. But because the system is volatile, we can only know for sure tomorrow [Friday] morning when we get feedback from the system operator," Eskom spokesperson Khulu Phasiwe said.
The embattled power utility implemented stage 2 load-shedding on Thursday afternoon, kicking in between 3pm and 11pm. This after stage 1 load-shedding had been in place from Thursday morning.
Eskom said the load-shedding was due to plant breakdowns, which resulted in an imbalance between supply and demand.
Reuters reported that a unit at Eskom's faulty Kusile power station tripped, adding to a shortfall of generating capacity.
Eskom group executive for generation Andrew Etzinger told Reuters that about 12,000MW of the utility's roughly 45,000MW capacity was offline on Thursday due to unplanned outages at some of the company's coal-fired power stations.
"Insufficient maintenance in recent years means many of our coal power stations are experiencing failures. Supplies of diesel are also under pressure," Etzinger said.