The death toll from a building that collapsed last Monday in South Africa's southern coastal city of George has reached 24, local authorities say.

Efforts continue to rescue and recover 28 other people who remain trapped under the rubble.

Among those still trapped is Florence Kawunga, a 19-year-old woman who had been employed at the site as a cleaner, her family told the News24 website.

81 people were in the partially-constructed, five-storey building when it fell.

Out of the 29 survivors who have been rescued, 13 remain hospitalised.

The cause of the collapse is being investigated.

The rescue effort includes 200 people with sniffer dogs, heavy lifting equipment and rescuers removing concrete blocks and debris by hand.