City Power in Johannesburg announced on Wednesday morning that Eskom cables feeding electricity to substations had been stolen during load shedding, causing blackouts in Lenasia and parts of Randburg.
At 09:30 on Wednesday the utility said it was still unable to restore power to these areas.
The lack of power has caused major traffic snarl-ups.
"Both Eskom and City Power are working to ensure we restore power as soon as possible," said City Power.
It expects to be able to restore power to some areas along Lenasia south in the morning.
This comes as Eskom has instituted another day of stage 4 load shedding as it battles a shortfall of available capacity.