A video shows music fans crouching and fleeing in panic as shots rang out at a country music festival in Las Vegas.
The mobile phone footage was posted online by vincestagramen shortly after more than 500 people were killed and dozens of others injured during a shooting at an outdoor music festival on the Las Vegas Strip.
Dozens of patrol vehicles descended on the Strip after authorities received reports of an active gunman near the Route 91 Harvest Festival.
Las Vegas police later said one suspect was "down" and they did not believe there were any other gunmen. Early reports said two people had died but later Las Vegas Police Department said the death toll was more than 20. Then a revised update said more than 50 had died and 200 were injured.
Concert-goers reported seeing muzzle flashes from the upper floors of the Mandalay Bay Hotel and Casino across Las Vegas Boulevard from the music festival and the sound of what they described as automatic gunfire.
Twenty-six people were admitted to the University Medical Centre, hospital spokeswoman Danita Cohen said. Of those, at least two died, 12 were in a critical condition and the rest were being assessed, she said.
Kodiak Yazzie, 36, said he and his girlfriend were watching country star Jason Aldean's performance when he heard what sounded like fireworks. The music stopped temporarily and then started up again before another round of pops sent the performers ducking for cover and fleeing the stage.
Thousands fled as bursts of gunfire could be heard for more than five minutes, Mr Yazzie said.
Witnesses said they saw multiple victims and dozens of ambulances near the concert venue. Some attendees later huddled in the basement of the nearby Tropicana hotel-casino.
Officers carrying assault rifles ran into the Mandalay Bay Hotel and Casino.
Authorities shut down part of the Las Vegas Strip and Interstate 15.
Flights were temporarily halted at McCarran International Airport because of the shooting, the airport said on its verified Twitter account.