The shack fire in Stjwetla, Alexandra, has been contained, City of Johannesburg emergency medical services (EMS) said on Tuesday afternoon.
EMS spokesperson Nana Radebe said over 100 shacks were destroyed in the blaze.
She said disaster management teams were on the scene to see how many people were displaced.
"Disaster management is working very hard to make sure that everyone that does has a place, can be helped."
As the rain continued to fall, several residents were trying to salvage their belongings.
No injuries have been reported.
The fire broke out at around 1.30pm on Tuesday. City Power spokesperson Isaac Mangena said an electricity pylon and its overhead lines 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.
"We are just waiting for EMS to finish so that we can investigate."
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