A nighttime fire ripped through a rundown five-story building in Johannesburg that was occupied by homeless people and squatters, leaving at least 73 people dead early Thursday, emergency services in South Africa’s biggest city said.

Some of the people living in a maze of shacks and other makeshift structures inside the derelict building threw themselves out of windows to escape the fire and might have died then, a local government official said.

A witness said he saw people throwing babies out of the burning building in an attempt to save them and that at least one man died when he jumped from a window on the third floor and hit the concrete sidewalk “head first”.