A 53-year-old woman, Patrizia Della Ragione, became the third casualty when she died of her injuries in the city’s Cardarelli hospital.
Her 29-year-old son, Roberto Abbruzzo, and her 35-year-old niece, Margherita Della Ragione, also died in the collapse.
Two more of Della Ragione’s children, Giuseppe and Luisa Abbruzzo, aged 34 and 23 respectively, are among 12 people who were injured.
The injured include seven children, two of whom are in a critical condition.
Prosecutors have opened an investigation into the collapse.
The 800 residents of the Vela Celeste (Sky Blue Sail) building where the collapse took place had to be evacuated, with the civil protection department setting up tents.
Around 300 people will be allowed to return to their homes once safety checks are done and water supplies are restored after some pipes were broken in the collapse.
But accommodation will need to be found for the other 500.
In Scampia, several other ‘Sails’ apartment buildings have been torn down over their state of decay.
ANSA