Videos have been posted online of Slipknot stopping a show to allow paramedics into the crowd as young women "started to get trampled and have seizures".
The metal band was performing in San Bernardino over the weekend as part of its Knotfest Roadshow 2019 tour when things got dangerous.
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Slipknot frontman Corey Taylor is seen in the videos yelling at the audience to move back and make space.
"Back the f**k up! No one is f**king getting hurt on my f**king watch," he shouts, as the band stop playing music.
"Do you understand me? Back the f**k up! Now give me a scream, motherf**kers!"
The footage was posted on Reddit, with disturbing accounts of how scary the show became for attendees.
"Kids and females were on the ground, hurt or unconscious, while people were still running around over them," claims mSTH95.
"If Corey hadn't stopped the song it could of been worse."
One of the videos was posted by user mSTH95, who describes the concert as "crazy f**king good".
"Mosh pits were so f**king rowdy, crazy good but some chicks started to get trampled and have seizures," they say.
"Corey got mad, he stopped the song because people wouldn't stop moving to get [paramedics] in."
More footage was posted by Reddit user Horrordave76, which he says shows one of the crush victims.
"So the girl I zoom in on was getting crushed, so much so they could not pull her out. It was a good minute before Corey stopped the band and I started recording. It was kinda scary."
Other Reddit users describe a man falling over in the mosh pit, being knocked out cold and bleeding from a head injury.
"I was seriously worried this dude was going to die down there," claims Reddit user MalnutritionUSA.
"Once we got him up, he kept going back out of consciousness and almost falling back down... we saved that dude."
Slipknot's setlist at their recent North American shows is as follows:
- People = Shit
- Get This
- Before I Forget
- The Heretic Anthem
- The Devil in I
- All Out Life
- Spit It Out
Slipknot is coming to New Zealand in October to play support for Metallica.