Joburg Emergency Management Services spokesman Nana Radebe told The Citizen that two of the adults and the baby had died of smoke inhalation while inside the building on the corner of Jeppe and Nugget Streets at about 4.30am on Saturday.
She added that the third adult had died as a result of “multiple fractures” after leaping from the blazing building’s seventh floor.
Three other people remain in serious, but stable conditions in hospital.
“The cause of the fire couldn’t be determined due the extent of the damage to the block,” said Radebe.
“The block on the seventh floor was initially built for offices, before it was used for residential purposes. We suspect that the cardboard divisions used to separate the apartments were the reason why the fire spread so quickly.”
Gauteng police couldn’t confirm that a case of arson was being investigated, after witnesses claimed that a man had doused an apartment with petrol and set it alight, according to reports.
A study by the Royal Institution of Chartered Surveyors found that there existed a “lapse in design provisions” for fire safety in older commercial buildings in Johannesburg.