More than 40 others are injured.
Johannesburg officials say it is unclear what sparked the blaze at the five-storey building in the city centre.
A spokesman for the emergency services, Robert Mulaudzi, told the BBC that firefighters had been able to bring out some of the occupants.
He said the fire had gutted the building, and that the search for other victims was continuing.
“We are moving floor by floor conducting these body recoveries,” Mr Mulaudzi told local broadcaster ENCA.
A video posted to the platform X, formerly known as Twitter, by Mr Mulaudzi showed fire trucks and ambulances outside the building with burnt out windows.
Photos from the scene showed covered bodies lined up near the burned building.
The building is located in what was formerly a business district in South Africa’s economic hub. It was being used as an informal settlement, Mr Mulaudzi said.
Local reports say the inner city neighbourhood is infamous for ‘hijacked’ buildings, a term used in South Africa to refer to buildings illegally taken over by undocumented migrants.
They also suggest the occupants of the building were mostly migrants from other African countries.
In the wake of the fire, many South Africans on social media have condemned the online xenophobic attacks that some have made against the victims and survivors of the fire.
Source: www.bbc.com
