Eskom moved to stage 2 load shedding at 15:00 on Thursday, after implementing stage 1 load shedding at 11:00.
The power utility's spokesperson Khulu Phasiwe tweeted an update at 14:30 to say that stage 2 load shedding would be implemented in the afternoon.
No further details were given.
Stage 1 load shedding allows for up to 1 000 MW to be shed from the grid, while stage 2 allows for 2 000 MW to be cut.
Earlier in the day, the power utility said that power rationing would be implemented "due to plant breakdowns, resulting in an imbalance between supply and demand".