Fans using their phones to record a concert in Las Vegas on Sunday became unwitting witnesses to the worst mass shooting in modern American history, as the chatter of automatic weapon fire interrupted a performance by singer Jason Aldean.

Videos posted online show the moment when joy turned to terror at the country music festival outside the Mandalay Bay Hotel and Casino, where a lone gunman perched at a 32nd-floor window opened fire on the crowd of thousands. Police say at least 58 were killed and more than 515 were injured in the attack. The shooter, who has been identified as Stephen Paddock, also died at the scene.

Canadians Quinn Mell-Cobb and his wife, Madison Milford, say they escaped the concert without injury, but that it was a chaotic scene.

Mell-Cobb said it took a few seconds after the first shots were fired for people to realized what was going on.

"We heard a bunch of pops in quick succession," he told 麻豆传媒 Channel on Monday. 鈥淓verybody was kind of startled around us but nobody thought it was anything but firecrackers or something like that, so everybody just ignored it.鈥�

But people clued in quickly after the second barrage of bullets, he says. 鈥淭here was a gentleman behind us who said, 鈥楾hat鈥檚 gunshots, everbody get down,鈥欌�� he recalled.

Mell-Cobb says his wife hit the floor but he hesitated for a moment, before throwing himself on top of her as another round of shots rang out. He says the man behind him pointed out that the gunshots were coming from the hotel, but the echoes off the buildings made it hard to be sure. 鈥淚t sounded like it was coming from everywhere.鈥�

鈥淗onestly, I thought it was going to be鈥� one bunch of shots,鈥� Milford said.

Mell-Cobb and Milford joined the stampede of fleeing people as they escaped the festival grounds and poured out onto the streets. 鈥渢here were people jumping on the cars, slamming on the hoods, telling people there鈥檚 a shooter,鈥� he said.

The two are now looking forward to catching a flight back home to Vancouver.

GRAPHIC WARNING: SOME OF THESE VIDEOS CONTAIN DISTURBING CONTENT AND OFFENSIVE LANGUAGE

The following video from concert-goer Hannah Dorfman shows Aldean鈥檚 on-stage performance at the moment when the shooting begins. The tat-tat-tat-tat of gunfire can be heard just five seconds into the video, unbeknownst to the singer or, apparently, the individual making the recording. The rattle of what sounds like a second automatic weapon can be heard partway through the brief video, ringing out at the same time as the first weapon. Aldean suddenly recognizes the sound and bolts off stage.

Other videos posted online show the chaos and panic that followed the shooting.

One video recorded from a window of the Mandalay Bay hotel, which has been verified by Storyful, shows concert-goers scattering across the festival grounds below. Dozens of bodies can be seen on the ground.

鈥淭here鈥檚 people laying there,鈥� a woman says in the video.

A video posted on Instagram captures the terror of concert-goers in the line of fire. People can be seen huddling on the ground or cowering together with the Mandalay Bay hotel visible in the background, moments after the first shots have been fired. More shots ring out a few seconds into the video, triggering renewed chaos as people flee or hit the ground for cover. The shooting stops briefly, then starts again.

 

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Another Instagram video shows the scene from inside one of the music festival tents after the first shots were fired. 鈥淭hat was an AR (automatic rifle),鈥� a man鈥檚 voice says. The shooting starts again and nearly everyone under the tent, including the person recording the video, hits the ground to take cover.

鈥淪cariest moment of my life,鈥� user rtbleck wrote in the caption on the post. 鈥淭hey just kept firing and firing.鈥�

 

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Facebook user Diane Yvette Navarro provided an on-the-ground look at a mob of confused concert-goers huddled together behind a barrier after the shooting started. Most are on the ground, although a few can be seen standing and looking over the barrier at the Mandalay Bay hotel. A security guard can also be seen behind the barrier. He shrugs as the camera pans past him, a second before the shooting starts again.

鈥淭hat鈥檚 not a gun,鈥� one man says, in apparent disbelief, as the gunshots ring out. 鈥淚t鈥檚 not a gun.鈥�

A chilling video recorded from a street corner near the shooting shows a woman staring in disbelief as two men and another woman tell her to take cover.

鈥淵ou might want to get inside because that鈥檚 gunfire,鈥� one man tells the woman, who has her cellphone to her ear.

鈥淭hat鈥檚 a machine gun,鈥� says the other, as sirens blare in the background and police car after police car whip past. The Mandalay Bay hotel is also visible.

鈥淕et inside,鈥� the first man says, before the steady, uninterrupted rattle of gunfire is heard once more.

The individual who posted the video says he had just left the concert in an Uber when he heard the gunshots.

 

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Witnesses from the edge of the scene shared videos of a massive police and paramedic response to the shooting.

A shelter in place order was in effect and police locked down the area following the overnight massacre. CTV National News senior broadcast producer Rosa Hwang, who is in Las Vegas, says the famous Las Vegas Strip and casinos were empty for hours.