The attack in the Nile Delta town of Tanta comes just weeks before Pope Francis is due to visit Egypt.
Egyptian media showed footage from inside the church, where a large number of people gathered around what appeared to be lifeless, bloody bodies covered with papers.
Health Ministry spokesman Khaled Megahed confirmed the toll from the attack in interviews with local and state-run media, AFP reported.
No-one immediately claimed responsibility for the attack.
A local Daesh (ISIL) affiliate claimed a suicide bombing at a church in Cairo in December that killed around 30 people — mostly women.
A militant group called Liwa al-Thawra claimed responsibility for an April 1 bomb attack targeting a police training center in Tanta, which wounded 16 people.
The group, believed to be linked to the outlawed Muslim Brotherhood, has mainly targeted security forces and distanced itself from attacks on Christians.
Egypt has struggled to combat a wave of radical militancy since the 2013 military overthrow of elected president Mohammed Mursi.