Emergency Management Services said another 43 people were injured in the blaze, which broke out early on Thursday.

The building has been evacuated, and spokesperson Robert Mulaudzi said a search and recovery operation was underway. It was likely the death toll would rise, he said, and it was not immediately clear what caused the blaze.

Inside the five-storey building was “an informal settlement”, Mulaudzi said. “So there [are] a lot of informal structures inside the building. There is a lot of debris which we have to remove.”

Authorities said the fire had been largely extinguished, but smoke still seeped out of the blackened building in downtown Johannesburg.

Television footage showed fire trucks and ambulances outside the red and white building with burned-out windows, which had been cordoned off by police