Forensic experts investigate mysterious origin of Johannesburg fire (Image: Getty)

       A day after one of the most devastating building fires in South Africa's history, families in Johannesburg have been rummaging through mortuaries searching for their loved ones.

       At least 76 people were killed in the fire, including 12 children.

       Many of the victims are thought to be undocumented migrants attempting to subsist on the outskirts of South African society.

       Earlier in the day, firemen returned to the structure to look for any other bodies.

       Although the origin of the fire has not been determined, forensic experts have been on the scene sifting through the charred remnants of the destroyed block.

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       Victims of Johannesburg blaze include twelve children (Image: Getty)

       The government has promised to help all victims, but many will face difficulties because they lack proper documentation within the country.

       Some are concerned that coming forward may expose them to law authorities.

       According to the Malawian foreign ministry, 20 Malawians are among the dead.

       On Thursday evening, President Cyril Ramaphosa visited the downtown Johannesburg scene and described the tragedy as a "wake-up call for us to begin to address the situation of housing in the inner city".

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       The structure was once utilised as a sanctuary for battered women and children. However, after the lease expired, it was "hijacked" by others, as President Ramaphosa told the media.

       Several properties in the area of the fire have been designated unfit for human habitation.

       Nonetheless, these ageing facilities, abandoned by their owners or city officials, are occupied by families, who frequently pay rent to the criminal organisations that oversee them.

       Undocumented migrants, particularly from other African countries, are among the occupants.

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       Many of these structures resemble pop-up slums, with weak barriers separating living spaces.

       Many witnesses said in the immediate aftermath of the fire that they were separated from family members in the chaos of escaping the inferno.

       Some said there were children walking around alone outside the building, with no idea if their parents or siblings had survived.

       Non-governmental organizations stepped in to help survivors with temporary accommodation, while religious leaders held prayer services outside the burned-out building.

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