Egyptians gather in front of a Coptic church that was bombed on Sunday in Tanta, Egypt, April 9, 2017. [Photo/Agencies]

Thousands gathered outside the church in Tanta shortly after the blast, some wearing black, crying, and describing a scene of carnage.

"There was a huge explosion in the hall. Fire and smoke filled the room and the injuries were extremely severe," a Christian woman, Vivian Fareeg, said.

President Abdel Fattah al-Sisi and Prime Minister Sherif Ismail are set to visit the Tanta site on Sunday and Sisi has ordered an emergency national defence council meeting, state news reported.

A shift in Islamic State's tactics, which has waged a low-level conflict for years in the Sinai peninsula against soldiers and police, to targeting Christian civilians and broadening its reach into Egypt's mainland is a potential turning point in a country trying to prevent a provincial insurgency from spiralling into wider sectarian bloodshed.

Egypt's Christian community has felt increasingly insecure since Islamic State spread through Iraq and Syria in 2014, ruthlessly targeting religious minorities. In 2015, 21 Egyptian Christians working in Libya were killed by Islamic State.

Reuters