At least eight people have died and scores of people have been hurt after a crowd surge on the opening night of a music festival in Houston, Texas.
Panic broke out after the crowd began to press towards the front of the stage at rapper Travis Scott's Astroworld Festival, emergency officials said.
Eleven people were taken to hospitals in cardiac arrest and eight died. Some casualties are aged as young as 10.
Some 50,000 people attended the outdoor event, which has been cancelled.
Lina Hidalgo, the county judge of Harris County, described what had happened as an "extremely tragic night".
"Our hearts are broken," she said. "People go to these events looking for a good time, a chance to unwind, to make memories - it's not the kind of event you go to where you expect to find out about fatalities."
Astroworld said in a statement that their hearts were with the "festival family... especially those we lost and their loved ones", and they thanked local emergency services for their response.
The incident began around 21:15 on Friday, Houston Fire Chief Samuel Peña said.
"The crowd began to compress toward the front of the stage, and people began to panic," he told reporters.
As the crush began causing injuries to people, the panic grew, the official added.
According to the Houston Chronicle, Travis Scott, who founded the festival, stopped multiple times during his 75-minute performance when he spotted fans in distress near the front of the stage.
The rapper asked security to make sure they were okay and help them out of the crowd. Emergency vehicles, lights and alarms flashing, cut through the crowds several times, the report said.
Fans pressed up against each other near the front of the main stage, eyewitnesses told the Chronicle. In some places, people were so crammed together that they started hyperventilating or struggling to leave.
Some 300 people were treated for injuries such as cuts and bruises on Friday. Judge Hidalgo said "many" of those killed at the festival had been "tragically young".
A reunification centre has been set up at the Wyndham Houston Hotel for families who have not heard from loved ones at the festival.
Saturday was to have been the second and final day of the festival.
"Nobody could dream of this," said Houston Police Department Chief Troy Finner. "But we're here, and I think it's very important that none of us speculate. Nobody has all the answers tonight."