Diamond company Petra Diamonds stopped operations at three of its mines on Monday evening after receiving a request from Eskom to reduce its load.
In a statement Petra said it was in the process of bringing its mining operations in Cullinan, Finsch and Koffiefontein to a halt to help Eskom conserve power.
"Production, hoisting and processing have stopped with immediate effect and the company is now removing all people from underground, except those required for essential services, with only pumping to prevent flooding and ventilation for safety being allowed.
"Petra will update the market as soon as it receives further notification as to how long the load curtailment will last, and therefore what impact this is likely to have upon the Company's production performance," it said.
Petra Diamonds is not the only mining company affected – BusinessDay reported that Impala Platinum and Harmony Gold have stopped operating at night.
Harmony Gold on Tuesday morning issued a notice to shareholders confirming that it halted overnight operations on Monday, and will do so again on Tuesday.
"Harmony Gold Mining Company confirms that, in response to a request received from power utility Eskom late yesterday afternoon, it has reduced power consumption at its South African operations to levels required only for the maintenance of emergency services.
"In the interest of safety and due to reduced power supply, night shift employees at Harmony’s South African underground operations did not go underground last night and today’s day shift employees, similarly, will stay on surface," the notice read.
“We will resume shifts as soon as Eskom is able to provide us with the assurance that power supply will be more reliable,” said Harmony chief executive Peter Steenkamp.
On Monday, Eskom announced it had taken the unprecedented decision to implement stage 6 load shedding – which allows for 6 000MW to be cut from the national grid. The decision was because of flooding at three power stations, which compounded the problem of unplanned outages at a number of other stations.
Eskom Chief Operations Officer Jan Oberholzer told eNCA in an interview on Monday evening that over the past eight days the utility had lost in excess of 12 units.
Public Enterprises Minister Pravin Gordhan, meanwhile, told eNCA that another 4 000MW of spare capacity needs to be brought in to stabilise the system.
The department of public enterprises is in the process of engaging with the department of mineral resources and energy to find out how best to do that, he said.
President Cyril Ramaphosa said in a statement on Monday evening that Eskom's immediate priority was to "get as much generating capacity back on line within the shortest possible time".
"Eskom's emergency response command centre and technical teams are working around the clock to fix multiple breakdowns," Ramaphosa said.