Harrowing footage shows festivalgoers appearing to dance on ambulances at Astroworld, where at least eight were killed in a fatal crush.
The tragedy unfolded as rapper Travis Scott was onstage, with hundreds suffering injuries.
One outraged Twitter user shared footage that seemed to show a man dancing on top of a buggy with flashing lights, which paramedics used to get to those who were hurt.
They wrote: "This getting outta hand that’s an ambulance."
Another separate video taken from the crowd shows three people on top of an ambulance vehicle, with the person who posted it writing: "people were dancing on top of the ambulance... yea go on ahead and cancel this s*** forever."
Victims of the tragedy were as young as 10, according to reports.
Distressing footage on social media shows paramedics performing CPR on several people on the floor within the crowd as a performance continued on the stage.
The fire department transported 17 people to hospitals with 11 of them in cardiac arrest.
The tragic scenes unfolded on the opening night of the third Astroworld music festival which was being held at NRG Park in the American city.
Earlier dozens of ticketless fans had stormed the gates of the highly-anticipated event, which was put together by rapper Travis Scott.
Scott was onstage performing a set which included a guest appearance from rapper Drake when the fatal crush occurred.
Officials said a crowd began to rush towards the stage at about 9.15pm local time and revellers began passing out because they couldn't breathe, KHOU reported.
Within 15 minutes, overwhelmed officials had declared a mass casualty incident because there were so many victims.
Houston Fire Chief Samuel Pena said hundreds of people were treated at the scene for injuries.
"The crowd began to compress toward the front of the stage, and people began to panic," he said.
One devastated festivalgoer posted on Twitter : "I saw people die before me and i heard people crying in disbelief of what they were seeing."
The remainder of the festival has been cancelled.
Dozens of emergency vehicles, including multiple ambulances, were on scene.
