At least 130 were wounded, the Gulf News reported.
Al Azhar, Sunni Islam's leading centre of learning, has condemned the attack on the mosque.
"Shedding blood, desecrating houses of God and terrorizing worshippers are corrupt deeds, which must be struck hard and firmly. After targeting churches [by militants], the turn has come for mosques as though terrorism wants to unify Egyptians in death and devastation. But terrorism will be routed," head of Al Azhar Shaikh Ahmad Al Tayyeb said in a statement.
President Abdul Fattah Al Sissi has called for an emergency security meeting soon after the attack, the state television reported.
An explosion reportedly took place inside the mosque when worshippers were carrying out their afternoon prayers.
Following the explosion, gunmen arrived in cars and opened fire at the fleeing crowd.
According to sources, most of the people who came for prayers were friends and family of the security forces.
The injured have been rushed to hospital.
No group has so far claimed responsibility for the attack. (ANI)