Several areas in Gauteng were left without electricity following a fire at the Observatory substation on Saturday morning.
In a statement, City Power said teams embarked on an emergency isolation plan from around 3am.
"A thorough Investigation to determine the cause of the fire and the actual extent of the damage will be conducted once the fire has been extinguished," the provider said.
City Power spokesperson, Isaac Mangena, said most of the equipment inside the control room was damaged in the blaze.
He said mop up operations are underway and a team is working to ensure that electricity is restored.
"Most of the damage happened on the underground cables and these cables need to be taken out to ensure that the area is cleaned and repaired," he said.
Mangena said this will take five to seven days to repair.
Yeoville and surrounding areas