Search and rescue efforts were going on, the city administration said on the platform X, formerly known as Twitter.

“The City of Johannesburg Emergency Management Services can confirm that the number of fatalities has gone up to 63,” it said.

Firefighters and emergency vehicles were at the scene, while bodies lay covered in emergency blankets on a street near the site of the early morning blaze, Reuters photographs showed.

Media said the fire engulfed a five-storey building that had been abandoned at one stage but where people had been living. It was not immediately clear what caused the fire.