At least 41 people died in a fire in a Coptic church in the greater Cairo area.
This was announced by the country's church on Sunday, at the same time medical circles in Egypt confirmed the same number of deaths to the German Press Agency.
14 other people were injured.
Local media published images of a burned-out room full of pews and pictures of saints on the wall.
The fire reportedly broke out towards the end of a Sunday morning church service in Giza, in the Greater Cairo area.
The interior ministry said a faulty air conditioner on an upper floor of the church caused the fire.
According to the private newspaper "Al-Masry Al-Youm", eyewitnesses said that a short circuit had occurred there after a power failure.
In Cairo on Sunday, the temperatures around 35 degrees Celsius, which are usual for August, prevailed.
President Abdel Fattah al-Sisi called Copt Pope Tawadros II to express his condolences.
The country's authorities would provide all support after the tragic incident.
According to the Ministry of Health, 30 ambulances were deployed to take care of the victims and take them to nearby hospitals.
The ambulances arrived at the scene of the fire minutes after the emergency call and took 55 people to hospitals.
After about two hours, civil protection brought the fire under control.
A team from the public prosecutor's office also set out to investigate the scene of the fire and to further clarify the exact cause.
More than 100 million people live in Egypt.
Around ten percent of the population is of Christian faith, most of them Copts.