Egypt's president has declared a three-month state of emergency after suicide bombers struck at two Coptic churches, killing 44 people at Palm Sunday services.

The attacks, in the northern cities of Tanta and Alexandria, also left more than 120 people wounded and came at the start of the Holy Week leading up to Easter, just weeks before Pope Francis is due to visit.

So-called Islamic State have claimed responsibility for the attacks.

It was the single deadliest day for Christians in decades and the worst since a bombing at a Cairo church in December killed 30 people.

Abdel Fattah al-Sisi announced he would be calling a three-month state of emergency just hours later and ordered military troops to be deployed across the country in the wake of the attacks.

His plans were approved by the government's cabinet, which said it will go into effect at 1pm Tuesday afternoon.

A suicide bomber tries to walk into St. Mark's Coptic Cathedral. Credit: Egyptian Interior Ministry

The president's office said in a statement: "President Abdel Fattah al-Sisi the Supreme Commander of the Armed Forces has ordered units from the military to immediately deploy and assist the civilian police in securing vital facilities in all provinces of the republic."

Parliament still must vote to uphold the declaration, a virtual certainty since it is packed with supporters of the president. It cannot exceed six months without a referendum to extend it.

The first bomb exploded inside St. George's Church in Tanta, killing at least 27 people and wounding 78, overturning pews, shattering windows and staining the whitewashed walls with blood.

Footage broadcast on CBC TV from inside the church showed a large number of people gathering around what appeared to be lifeless bodies covered with papers.

People outside the church in the Nile Delta town of Tanta, Egypt. Credit: AP

A few hours later, a suicide bomber rushed toward St Mark's Cathedral in the coastal city of Alexandria, the historic seat of Christendom in Egypt, killing at least 17 people and wounding 48.

CCTV images showed a man with a blue sweater tied over his shoulders approaching the main gate to St Mark's and then being turned away by security and directed toward a metal detector.

He passed a female police officer talking to another woman, and entered a metal detector before an explosion happened.