South Africa's electricity system is severely constrained and will remain so until at least Thursday, although rotational blackouts to avoid tripping the grid are not expected, state utility Eskom said late on Monday.

Eskom was forced to implement rolling power cuts – or load-shedding – earlier this year and for a week last month as some of its generating units failed.

The entity is saddled with a creaking infrastructure due to years of poor maintenance.

"The system remains vulnerable to a number of variables due to historic factors such as inadequate maintenance, as well as ageing of plant. The unexpected loss of additional units may result in load-shedding at short notice," it said on Monday night.

Unplanned breakdowns were currently above the critical threshold of 9500 MW, necessitating the extensive use of emergency resources (water and diesel) in order to meet demand, Eskom added.

The company urged consumers to use electricity sparingly by switching off geysers as well as all non-essential lighting and electricity appliances.