Coptic Christians were in mid-prayer Sunday when the ear-splitting blast tore through their church in
"It was terrifying. Things were falling down on us. I couldn't get down from behind the altar because of the smoke," said church volunteer Tadros Zaki, 63.
"There were too many people. Destroyed, in pieces... people on top of people," said Romany, who rushed to the church to help after the bombing.
The health ministry said at least 25 people were killed.
The focal point of the explosion at the Saint Peter and Saint Paul Church appeared to have been just inside the entrance, on the side where the women sat.
A woman's scarf, drenched in congealing blood, lay in the wreckage.
The stone recess above the door was peppered with shrapnel which also left holes in the marble floor. A pew that remained upright was soaked in blood.
Two nearby boxes, one that had been filled with written prayers left by worshippers and another that held a saint's relics, were destroyed.
Dazed priests paced the arcaded courtyard, pieces of stained glass from the church's windows crunching underfoot, as guards at the doors blocked a crush of journalists and concerned faithful.
One nun in a grey habit stared pensively at the wreckage.
"God will have a say in this," she decided.
Bishop Angaelos, the General Bishop for the Coptic Orthodox Church in Britain, told AFP by telephone that Saint Peter's church was especially popular with parishioners.
It is "is deeply loved by many Coptic faithful in Cairo and it has a regular parish presence," he said.
"The fact that they were targeted this way when they were going to pray is beyond comprehension."
Copts have been attacked before in Egypt, most notably in a suicide bombing that killed more than 20 congregants at an Alexandria church in 2011.
But Saturday's attack hit close to the heart of the beleaguered minority's faith.
The church is adjacent to Saint Mark's Cathedral, the seat of the Coptic Christian papacy.
"What are we to do? God will dispense our affairs," said Magdy, a church administrator whose office is at the other end of the courtyard from the blast site.
The explosion shattered his office windows, leaving his desk strewn with shards of glass.
Outside, a growing crowd of Copts began chanting against the government, and there were brief scuffles with riot police who cordoned off the scene.
"The people want the downfall of the regime!" they chanted. "Hey, interior ministry! Where were you when they bombed the cathedral?"
Copts, who make up about 10 percent of Egypt's 90 million people, have suffered repeated attacks for decades.
jpegMpeg4-1280x720They also attracted the wrath of Islamist extremists after the church, along with Muslim religious leaders, supported the military overthrow of Islamist president Mohamed Morsi in 2013.
Mobs attacked scores of churches and Christian properties in August 2013 after police in Cairo killed hundreds of Islamists protesting against Morsi's overthrow.