The girl lies in a hospital bed, staring straight toward the ceiling. The left side of her face is swollen, her left arm wrapped in gauze.

In a preternaturally calm voice, she speaks on camera of how the gunmen in the Crocus City Hall music venue spotted her and a small group of people as they fled the carnage of the worst terror attack on Russian soil in decades.

“They saw us,” she told RT, a Russian state-funded news agency. “One of them ran back and started shooting at people. I fell to the floor and pretended to be dead. I was bleeding,” she said, pointing at her temple.

The gunmen opened fire into some of the bodies as they lay on the ground, she said.

“The girl lying next to me was killed.”

Islamic State has claimed responsibility for the attack. The four men, who appear to be from Tajikistan in central Asia, have been arrested, Russian police say.

The gunmen then set fire to the hall, apparently hoping to kill all those left inside.

“Then the flames flared up. They closed the front door, but they probably couldn’t close the lock,” said the woman, who did not give her name. “I was lying under the door, breathing air. After some time, I crawled out, three minutes passed, maybe four. I looked around, crawled to the exit. I realised that there was no one there and went outside.”

That was just one of the horrific stories to emerge in the deadliest terror attack in Russia since the 2004 Beslan school siege.

In videos and eyewitness accounts, a picture of terror and confusion emerges as the men burst into the concert hall firing automatic weapons, shooting at point-blank range into prone bodies, then stalked through Crocus City Hall on Moscow’s outskirts for nearly an hour as panicked concertgoers scrambled through the bowels of the building to find a way out.

The attack came minutes before the start of a sold-out concert by Piknik, a Russian rock band formed in Leningrad in the 1970s. Many concertgoers initially assumed the sound of gunshots was part of the show.

“At some moment we heard a large bang coming from outside the room, we thought it was part of the concert,” Arina, a 27-year-old clinical psychologist from Moscow, told the Guardian.

“But at some point, we understood that something was seriously wrong, we realised there were shootings.”

Soon after, Arina saw a man in camouflage clothing enter the concert hall holding an automatic rifle.

“We all lay on the ground. I looked beside me and I saw many injured people covered in blood.”

Arina described seeing a woman trying to talk to the man before being shot at point-blank range.

Arina said she eventually managed to escape the concert hall and then ran down an escalator.

“On the way down, I saw blood on the floor everywhere and many bodies. Some people tried to carry those who were unconscious,” she said.

Alexander, a witness in the concert hall, told Russian state media. “They didn’t say anything. They just started shooting at the people in front of them.”

Astonishingly, many people in the hall pulled out their mobile phones and caught footage of the gunmen methodically firing into the crowds, as well as the panicked reactions of others fleeing for the exits.

“Put your phone away and crawl!” one man can be heard screaming in footage posted online, as the gunmen fire into the crowds below the balcony. Some on the lower levels had to crawl out past the dead and wounded.

Emergency workers searching the building continued to find bodies into Saturday afternoon. At one point, according to the Baza telegram channel, 28 bodies were found in a single toilet, where people had sought shelter from the shooting. Another 14 bodies were discovered in an emergency stairwell.

One man described how he and others sheltered in a toilet that began to fill with smoke.

To escape to safety, they smashed through the plasterboard walls and lowered themselves down along the piping to the lower levels of the building, and then smashed through a window in order to escape on to the street.

From outside, those who escaped could still see people trapped in the building’s upper floors, banging their fists through windows or yelling out from the roof as the flames and smoke coming out of Crocus City Hall grew higher.

Yulia Kharitonova and her boyfriend were late to the concert. As they rushed into the hall just after 8pm, the gunmen opened fire.

“It turns out they were right behind us,” she told the Astra telegram channel. “We came in … and there were not many people there, [the attackers] shot and ran to where there were more people. I was shot in the shoulder, my boyfriend was hit in the arms and legs.

“A woman with a bullet through her temple fell right next to me,” she continued.

“A cheerful woman was selling tickets at the entrance, and when we ran away she was lying with these tickets with a bullet in her head. I still have this picture in front of my eyes.

“We ran over the bodies through the same doors [we came in through], we already heard sirens, the police and ambulances were coming.”