Workers continue the hunt for survivors after the building collapse in Cairo. (AAP)  At least seventeen people have been killed and three remain under the rubble after a residential building in Egypt's capital collapsed.  Countless buildings in the teeming city of more than 20 million have been put up in defiance of the most elementary rules of construction, often without permission, rescue services say.  The owners had illegally added two additional floors to the seven-storey building in the poor Matariya district in the east of the city.  "Seventeen people have been killed, eight injured and three are still under the rubble according to their relatives," Cairo's emergency services head General Mamduh Abdelkader told AFP on Tuesday.  He said the cause of the collapse was still being investigated but illegal construction work was suspected.  "We don't yet know the cause of the accident but we have been told that two storeys were recently added totally illegally," Abdelkader said.  Relatives of the missing and onlookers were digging with their bare hands in the rubble.  A woman who said her brother died in the collapse charged that the building was so unsafe she had refused to enter it.  "When I would come to see my brother I refused to come inside because the building was too fragile. I told my brother and all inhabitants they had to leave," she said.  Mohammed al-Bishlawy, district prosecutor for eastern Cairo, told AFP he has opened an inquiry and asked for the arrest of the building's owner.  He blamed the accident on "renovation work in a second-floor apartment that has affected the structure of the building and the addition of two floors without permission".  There have been several deadly building collapses in the past few years in Egypt, where safety and planning regulations are widely flouted.  Landlords often add extra floors to buildings whose foundations were not designed to support them.  Do you have any news photos or videos?
Investigators believe that a building collapse in Egypt that left at least 17 people dead may be the result of illegal construction work.