Eskom has announced unprecedented stage 6 load-shedding from 6pm on Monday.

The ailing power utility simply said this is due to a "shortage of capacity".

"This follows a technical problem at Medupi power station impacting additional generation supply," Eskom said on Twitter.

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Rainfall was also blamed.

"The heavy rains has caused coal handling and operational problems at several power stations," Eskom said.

However, it said this was not a cause for alarm.

"We remind and assure customers that load-shedding at stage 6 is no cause for alarm as the system is being effectively controlled. Stage 6 requires 6,000MW to be rotationally load-shed," said Eskom.

It continued in a Facebook post that Eskom's emergency response command centre and technical teams "will be working through the night to restore units as soon as possible".

"Eskom is working closely large industry to assist with further load curtailment. Load-shedding is a responsible act and highly controlled process, implemented to protect the country from a national blackout.

"After 2015, Eskom and the municipalities identified the need to extend the loadshedding stages up to stage 8 and the national code (NRS048-9 Ed 2) was subsequently updated.

"Even beyond these schedules, the system operator will reduce demand in a manner that is controlled," the post read.