A gunman who shot dead at least nine people outside a Coptic Christian church in Cairo calmly walked along the street unchallenged for nearly 10 minutes, video footage suggests.

In clips circulated on social media, the attacker is seen stopping only occasionally to fire at his pursuers in the Egyptian capital before being shot himself.

The sight of the Isis gunman displaying an assassin's calm contrasted with the congratulatory tone of pro-government media, whose coverage focused on how police "successfully" prevented him from breaking into the church on Friday and detonating an explosive device.

The videos, which emerged on Saturday, drew a flood of critical comments about the police's handling of the shooting and ridicule of authorities for heaping lavish praise on officers.

The Interior Ministry, which oversees the police, said the gunman was wounded and arrested, but the Health Ministry said he was shot dead. The discrepancy could not be immediately clarified.

It also remained unclear whether the gunman acted alone when he opened fire on Mar Mina church and a nearby shop, run by a Coptic Christian, in the Egyptian capital's southern suburb of Helwan.

The official Mena news agency quoted a top security official as saying the gunman was one of two attackers.

The Isis-run news agency, Aamaq, also claimed the attack was carried out by a "security detail", suggesting more than one assailant, and said one fighter was killed.

Security officials outside Mar Mina church following the attack (EPA)

"The alertness of security forces prevents a massacre at Mar Mina church," was the red banner headline in one pro-government daily, Al-Watan. The front-page headline in the state-run Al-Gomhuria daily tapped the same idea, declaring: "Alertness defeats terror and conspiracies."

Friday's attack came amid extraordinary security around churches and other Christian facilities in anticipation of violence on New Year's Eve and the 7 January Christmas of the Coptic Orthodox Church, Egypt's largest Christian denomination.

The killings were the latest in the long-running war between Isis-led militants and security forces that has been mostly fought in the Sinai Peninsula.

Hundreds of mourners took part in funerals for the Christian victims of the attack late on Friday.

Blood stains are seen on the ground from the victims killed in the attack (Reuters)

The attack's brazenness and brutality mirrored recent operations by militants, including the massacre last month of 311 people inside a mosque in what was the deadliest attack by extremists against civilians in Egypt's modern history.

Last week, they fired a guided rocket on the airport in el-Arish, northern Sinai's largest city on the Mediterranean, destroying a helicopter and killing at least one senior officer.

Significantly, that attack took place while the defence and interior ministers were on a previously unscheduled visit. Both escaped unharmed, but the attack showed an unusually high level of actionable intelligence available to the militants.

Most videos of Friday's gunman circulating on social media were filmed from windows in high-rise apartment blocks overlooking the street in which the church is located. The voices heard on the videos hurled insults on the gunman and expressed amazement at how calm he was.

Witness Mohammed Adel Hamza, who shot a 10-minute video of the gunman, said residents followed the gunman as he walked, taking cover behind trees and parked cars to avoid being shot.

"As soon as the gunman was shot and fell on the ground, they all started running toward him," he said.

"I saw people pelting the gunman with bottles and rocks, but he didn't point his gun at any of them," he said. "He started shooting as soon as the police appeared."

Mr Hamza's video and similar footage showed the gunman taking no notice of cars, motorbikes and, in some cases, pedestrians walking past him at close proximity. At one point, he appears to have had a conversation with a man riding a motorbike, but does not attempt to commandeer as his getaway transport.

"It was all a weird scene," said Mr Hamza.

On Saturday, Aamaq released a video that it said showed the militant before the attack. Masked, with a scarf showing only his eyes, he pledged allegiance to Isis leader Abu Bakr al-Baghdadi, urged militants in Sinai to stand fast, and vowed to avenge group members killed.

Egyptians gather for the funeral of the victims of the attack (AFP/Getty Images)

Egypt's Coptic Christians have been specifically targeted by the militants, who carried out a series of bombings against churches starting in December 2016, killing more than 100 and wounding scores.

The local Isis affiliate has claimed responsibility for all the bombings targeting Christians.

Christians make up about a tenth of Egypt's population. They have long complained of discrimination in the Muslim-majority nation and claim authorities have often failed to protect them from sectarian attacks.

Just last week, hundreds of Muslim demonstrators stormed an unlicensed church south of Cairo, wounding three people.

The protestors shouted anti-Christian slogans and called for the church's demolition, according to the local diocese. They destroyed the church's fittings and assaulted Christians inside before security personnel arrived and dispersed them.