Outside Cairo's main Coptic cathedral, crowds gathered in grief and anger.
Many in the crowd were furious about the deadly attack that no one had immediately claimed responsibility for.
The explosion took place in a chapel adjoining the main hall of Saint Mark's Cathedral, the largest in the metropolis of 20 million, where security is normally tight.
A reported 12 kilograms of TNT explosives were used, killing many women and children.
Egyptian endowments minister Mokhtar Gomaa has called on Egyptians to unite against terrorism.
"It is a stab in the heart of every Egyptian. God willing, together, Egyptians will eliminate terrorism and we will cut off the hand of the terrorist traitors. With one voice, we stress that this brutal terrorism must be eliminated."
The attack is one of the deadliest carried out against the religious minority in recent years.
The last similar attack was in 2011, when at least 21 died and at least 79 were injured after a car bomb exploded outside a Coptic church in the city of Alexandria.
But Egypt has suffered a rise in attacks by militant groups since the overthrow of president Mohammed Morsi, of the now-banned Muslim Brotherhood, in 2013.
And the country's Christian community has felt increasingly insecure since the self-proclaimed Islamic State spread control through Iraq and Syria in 2014, targeting religious minorities.
In 2015, IS killed 21 Egyptian Christians working in Libya.
One man in the crowd near the Cairo church says it is critical that people are able to rise above religious tensions.
"We're all one. There's no such thing as Muslim and Christian, there are only Egyptians. We pray that God will protect Egypt and that everything will get better."
The Australian Coptic Movement Association says the bombing is deplorable and unjustifiable.
Spokesman Peter Tadros says it is disheartening that a scourge of violence and intimidation continues to afflict the community.
"Coptic Christians are seen as a scapegoat, and some of them, some Islamists, even blame Coptic Christians for the ousting of the Muslim Brotherhood president. So, Copts are definitely one of the most vulnerable communities in the Middle East and in North Africa. And especially in Egypt, they are under threat at the moment."
