More than 60 people have died in a fire that engulfed a five-storey building in central Johannesburg on Thursday, the South African city's emergency services said.

Another 43 were injured, some suffering from smoke inhalation, and were taken for treatment at local hospitals, Emergency Management Services spokesman Robert Mulaudzi said.

"We are now on 63 fatalities and 43 people injured who were transported to various healthcare facilities," said Mulaudzi.

Firefighters at the scene had put out the flames and search and recovery operations were ongoing.

"We are moving floor by floor conducting these body recoveries," Mulaudzi told local broadcaster ENCA.

An AFP reporter at the scene said emergency services were continuing to bring charred bodies out of the building, laying them down under blankets and sheets on the street outside.

"It is indeed a sad day for the city of Johannesburg... over 20 years in the service, I've never come across something like this," Mulaudzi said.

It was not immediately clear what caused the blaze, which broke out overnight.

The building, which has been evacuated, is located in a deprived area of what used to be the business district of South Africa's economic hub, and was used as an informal settlement, Mulaudzi said.

"A lot of people" might have been trapped inside when the fire started, he added, suggesting many in the building may have been squatting illegally.

Fire trucks and ambulances were parked outside the red and white building with burned-out windows, which has been cordoned off by police, as a small crowd of onlookers gathered in the area.

Illegal occupation of disused buildings in the city centre is widespread, with many said to be under the control of criminal syndicates who collect rent from occupants.

In June a blaze ripped through a dilapidated building in Johannesburg and killed two children under ten who were locked in an apartment.