At first, it just sounded like fireworks.
The Sunday headliner, Jason Aldean, had taken the stage not 30 minutes before, and it seemed natural that on the final night of Las Vegas' three-day Route 91 Harvest music festival there would be some pyrotechnics. Even Aldean stayed on stage as the first loud bursts rang out above the crowd of some 22,000 people.
But after "quite a while," one concert vendor told Fox News, she and those around her understood something was wrong. It "was weird because we didn't see anything in the sky," she said.
"And then, the screaming started. And the running."
A gunman, perched in a Mandalay Bay hotel room 32 floors up, had opened fire on the crowd at about 10:08 p.m. local time, police said later. In the hours that followed, at least 58 people would die and more than 500 others would be injured. It was the deadliest mass shooting in modern U.S. history.
The gunman — identified by police as Stephen Craig Paddock, a 64-year-old white Nevada resident — was found by a SWAT team in the room, dead of an apparently self-inflicted wound. Officials say he was surrounded by at least 10 rifles, and they believe he acted alone.
In those opening moments of clatter and confusion, though, concertgoers knew nothing of this.
"I still thought that it was fireworks," Mia Uribe, who had been in the crowd, told NPR. "I heard someone yell 'gun!' — and everyone was running towards us, everyone was telling you to get down. There were people jumping over.
"It sounded like 'pop!' — over and over and over again, and it didn't stop," she added. "There was just continuous flashing light."
A couple named Gayle and Mike were huddled inside a merchandise tent at the time.
"I told my husband it's firecrackers," Gayle said to a local CBS affiliate. "He goes, 'No it's not, it's machine gun or something — an automatic rifle.' "
And as the gunfire kept on, they knew they had to do something. They just didn't know what. Everyone around them seemed to be running — but it didn't make sense.
"There was nowhere to run, because you couldn't tell where it was coming from."
There, in the tent with them, was a Las Vegas Metropolitan Police Department officer.
"He was yelling, 'Turn the lights off! Turn the lights off!' Because we were sitting ducks," Gayle said. "And you could hear the bullets coming closer. And then it would get quiet when they would reload and then they'd start going again."
A girl just a few feet behind them was shot in the stomach, Gayle said. Others reported seeing bloodied bodies strewn across the ground. Ricochets around them echoed the bangs from above, and still "no one knew where the gunfire was coming from," said journalist Mark Gray, who had been covering the concert for Rolling Stone.
"I smelled gunpowder," he said. "A lot of gunpowder."
Those who didn't run hid under the bleachers, under their seats, in beer trucks and vendor tents. Some people lay on others, protecting them from the gunshots, while first responders tried to usher people to safety.
Miguel Martinez-Valle, a reporter with Fox5 Las Vegas, had been eating dinner nearby when he heard the news. The festival had been set on a big, fenced-in lot — and the concertgoers he spoke to said those fences quickly came down as people tried to escape.
"People actually trampled the fences trying to get out, to run away from the area, and people didn't know which direction to go," he said.
"It sounded like machine guns. It sounded like more than one machine gun. It just didn't stop, like 30 minutes," a concert vendor told Fox News. "It was mass chaos. So we didn't know what to do."
The blasts seemed to go on for an eternity. Then, finally, the gunfire above them stopped. And those nightmarish sounds gave way to others: the screams of the wounded, and the sirens of those rescue workers struggling to save them.