Emergency services said the fire destroyed about 100 shacks. It broke out at around 1.30pm on Tuesday and has since been extinguished.
According to the city, over 30 firefighters were still at the site, damping down the affected areas to ensure that the blaze didn't flare up again.
"Disaster management continues to assess the damage caused. Relief operation planning is underway between the city’s disaster management and social development departments," the city said in a statement.
The Marlboro Indian community and NGOs such as Gift of the Givers, Alim Al-Imdaad and Ashraf Uloom, among others, will assist with relief aid.
City Power spokesperson Isaac Mangena said an electricity pylon and its overhead lines had collapsed, setting several shacks alight.
"We don't know what caused it to fall, because normally it stands firmly in the ground. The line carries about 88 kilovolts of electricity. It is just by luck that when it fell, it did not touch people," said Mangena.
Mangena said they would investigate the incident.