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Fans caught up in a crush where eight people died while watching Travis Scott at his Astroworld festival in Texas on Friday have described their panic.
Lucas Naccarati told BBC Radio 5 Live that within three minutes of the rapper coming on stage, he "was pretty sure people are going to be dying here".
"You couldn't move, you couldn't scratch your own face, [that's how] tight it was," he said.
The victims were aged between 14 and 27, with hundreds more hurt.
The music event is now under investigation by police and several concertgoers are suing Scott and the promoters for damages.
The star, who set up the annual festival in Houston, his home town, has said he is working to help victims' families.
Warning: The following contains distressing details
Mr Naccarati was "towards the front middle" section of the crowd.
He said: "People started trampling over everybody. I lost my shoes immediately.
"When everybody was starting to fall, I was blessed enough to unfortunately be stopped from falling because there were bodies under mine.
"I was barefoot. I stepped on someone's chest, and someone's shin or forearm, and I just had to step on them to keep myself up and get myself out of there."
After managing to extricate himself from the crowd, Mr Naccarati used first aid skills he learnt when he was in the US Marines and from his brother, who is a doctor.
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"A girl fell next to me. And she was falling and screaming for death. And that's when I started giving her CPR," he said.
"And then she came back. When I'd left her. She was alive so somebody else came to help her because I had to help another guy because he was dead when I was giving him CPR."
Mr Naccarati said the life-threatening situation was initially due to "how condensed we were together", but then "people were getting stepped on so when they'd lean forward, they would fall – they can't catch their balance".
He continued: "When they would fall it would cause a ripple effect for other people to start falling. And if you fall, it is physically impossible to get back up. Doesn't matter how strong you are, you will not get back up."
Image source, Getty ImagesImage caption, The festival first took place in 2018
Edward Figueroa, another attendee, told the BBC that fans "were packed like sardines".
"I have multiple videos of people passed out receiving CPR," he said. "I walked by multiple bodies while I was there but did not comprehend the magnitude of their situation.
"About two minutes after the initial surge, a large amount of people started clawing back out the crowd, almost all of them crying. I personally had a girl grab and hold onto me for dear life."
He added: "I don't think Travis Scott knew what was happening to the extent it was. He has always been for his fans and I've been following him since before any of his albums."
'We begged for help'
Another attendee, Seanna Faith, wrote on Instagram that she wanted to get as near to the front as she could but ended up in the middle, surrounded by chest-high metal gates.
"Within 30 seconds of the first song, people began to drown… in other people," she wrote.
"My friend began to gasp for air and she told me we needed to get out. We tried. There was nowhere to go.
"We began to scream for help. More people began to scream for help, some began to collapse. The music continued.
"We begged for security to help us, for the performer to see us and know something was wrong. None of that came.
"One person fell… once one fell, a hole opened in the ground. It was like watching a Jenga tower topple. There were people on the floor unconscious."
She managed to get to the back of the crowd and a man pulled her over a guard rail. Her friend also survived.
Ms Faith said she asked several members of festival staff to help, including by climbing onto a camera podium to plead with a cameraman.
She has said he called for help, and that was the reason two members of the medical team went to assist.
On Reddit, one user said the problems started earlier during rapper Don Toliver's set.
Others said they weren't aware of what was going on due to their position in the crowd.
"So many people were trying to push into the crowd and many got trapped at the front, trying to get out. Due to the pushing from both ends, nearly got crushed," one wrote.