Officials say the number of dead is at least 41, with dozens injured. Children are believed to be among the dead.

An electrical fire broke out as 5,000 worshippers gathered for Mass at the Coptic Abu Sifin church in Giza, security sources told Reuters.

The fire blocked an entrance, causing a stampede, they said.

Citing hospital records, CNN reported that some 18 children, aged between 3 to 16 years old, were killed.

Fire services said the exact cause of the fire remains unclear. However, Father Farid Fahmy, from another nearby church in the Imbaba neighbourhood, told the AFP news agency that it was sparked by a short circuit.

"The power was out and they were using a generator," he said. "When the power came back, it caused an overload."

Worshippers have been explaining their moments since the blaze ignited.

"People were gathering on the third and fourth floor, and we saw smoke coming from the second floor. People rushed to go down the stairs and started falling on top of each other," Yasir Munir told Reuters.

"Then we heard a bang and sparks and fire coming out of the window," he said, adding that he and his daughter were on the ground floor and able to escape.

The exact cause of the fire is not clear

Egyptian President Abdel Fattah al-Sisi offered his "sincere condolences to the families of the innocent victims that have passed on to be with their Lord in one of his houses of worship".

He has ordered the armed forces to rebuild the church.

The prosecutor's office said it had sent a team to the scene to investigate the cause of the blaze.

Giza lies just across the Nile from Cairo and is part of the Greater Cairo metropolis.

Coptic Christians make up at least 10 million of Egypt's 103 million people.

Copts claims they face discrimination and play a lesser part in Egyptian public life than their numbers justify.