South African firefighters have gone back inside the Johannesburg building destroyed by fire on Thursday to see if they can find any more bodies.

The blaze, in the overcrowded and condemned five-storey building, claimed 74 lives, including 12 children.

The fire service says it wants to be sure that no-one has been left behind.

The cause of the fire remains unknown but forensic investigators are also at the site picking through the charred remains of the burnt-out building.

Relatives who believe that family members may have been among the victims of the fire have been asked to visit the mortuary to help identify the bodies.

Visiting the scene in central Johannesburg on Thursday evening, President Cyril Ramaphosa called the tragedy a "wake-up call for us to begin to address the situation of housing in the inner city".

The building used to be a home for abused women and children, but once the lease expired, it was "hijacked", President Ramaphosa explained to reporters.

Many properties around the area where the blaze happened have been deemed unfit to live in.

Yet these old blocks, abandoned by their owners or the city authorities, are full of families, often paying rent to criminal gangs who run them.

Some of those who use the buildings include undocumented migrants, mostly from other African countries.