WARNING: Distressing content

One moment they were dancing at a country music concert, they next they were fleeing for their lives from the worst mass shooting in US history.

Haunting videos captured the moment joy turned to bloody tragedy for thousands of music fans as they were cut down by volleys of machine gun fire in Las Vegas.

The wounded were rushed to safety on office chairs, in wheelbarrows, and loaded into trucks and cars as the carnage unfolded.

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Russell Bleck, who witnessed the attack on the Route 91 Music Festival, told how some people plugged bullet wounds with their fingers.

He told NBC News: "I saw a lot of ex-military jump into gear and start plugging bullet-holes with their fingers.

"While everyone else was crouching I saw police officers standing up as targets, just trying to direct people and tell them where to go.

"The amount of bravery I saw there, words can't describe what it was like."

Speaking about the moment gunman Stephen Paddock opened fire, he added: "He was just spraying the crowd, it was relentless, there was no stopping, maybe five or eight seconds to move from cover to cover to try and get out as he reloaded."

Police say at least 58 people died and more than 515 were injured after Paddock, 64, attacked concert-goers with an "arsenal" of weapons from a room inside the Mandalay Bay Hotel.

Paddock was shot dead after police breached the room and got into a firefight with him. Two officers were wounded, one of whom required surgery.

Footage from the scene shows people hitting the ground near the front of the stage, either wounded or in an attempt to hide, as gunfire is heard in the background.

The shots can be heard getting louder and quieter as Paddock indiscriminately sprays a stream of bullets from side to side.

Other videos show thousands of people streaming away from the venue, while those unable to escape curl up behind whatever cover they can find.

Some described watching their loved ones die in their arms.

Brianna Hendricks, who was at the concert earlier in the night but had returned to the Mandalay Bay Hotel before the massacre took place, told Dailymail.com: "It was terrifying, we heard constant gunfire."

Another witness, who asked not to be named, added: "I was in room 135 and I heard over the police scanner that the shooting came from room 137.

"It was non-stop, I would say well over 100 rounds. We hit the floor and took cover.

"I called the front desk and she was remarkably calm and said she was aware of the situation and told us to stay in our room.

"After around 10-15 minutes it just kind of stopped. You could smell the gun powder.

"Right before we got out I heard an explosion, maybe a flash bang, but windows were blown out.

"The cops came on to the floor and they were clearing rooms room by room and six or seven cops came into our room and we were evacuated."

Other sobbing concert goers told DailyMail.com that the gunfire was so intense, it sounded like 4th of July.

Derek and Karen Bernard, from Los Angeles, California, were in town for the Route 91 country festival and were close to the stage when the shooting began.

"We were inside," said sales manager Derek, 53. "All of a sudden, we saw the band disappearing - they were like running off the stage.

"We were off to the left side of the stage, we were running off there and there were staff security there.

"There was a woman bleeding - that's when we realised it was real shots. She just fell. She was shot. There was a lot of blood.

"It was so many - it sounded like 4th of July - just pop, pop, pop, pop, pop. So many. I didn't think it was real because I couldn't see or feel anything. I was so panicked."

Wife Karen, a retired teacher, added: "We heard shots fired, it sounded like firecrackers. We thought it was part of the concert.

"People were saying get down, get down and so we did. It was like mass havoc, panic, people were trampling over each other trying to get down.

"People were saying get behind the stage, get down and we crawled behind the stage. The shots they started coming much louder and closer."

Describing their escape, she added: "We jumped behind the stage. Someone made a ramp up to the top of the wall - we crawled, jumped and they caught us. We didn't know where to go. There was just an exodus of people."