At least 19 people died and seven injured when a building collapsed in Cairo’s Matareya district in the early hours of Tuesday, Al-Ahram Arabic news website reported.
Others are still thought to be missing under the rubble.
The building is believed to have been inhabited by 25 people.
A preliminary inspection of the site by prosecutors showed the owner had added two extra floor to the building without planning permission, and the second floor was undergoing renovation at the time of the collapse.
Both of these factors could have contributed to the collapse, prosecutors said.
Only four of the six floors were occupied.
It is not uncommon for buildings to collapse in Egypt, often due to age, illegal extensions and failure to comply with building regulations.