Authorities said law enforcement swarmed the hotel and killed the gunman in a room on the 32nd floor.
Some concertgoers stayed behind to offer help to those around them.
“Everybody I saw breathing, I helped.” a concertgoer told Fox News.
Kodiak Yazzi, 36, said the music stopped temporarily and started up again before another round of pops sent the performers ducking for cover and fleeing the stage.
As the 40,000 fans in the crowd began to flee, Yazzi took cover and said he saw flashes of light coming from the Mandalay Bay hotel tower high above.
The area is now on lockdown. All clubs and businesses on the strip are closed.
University Medical Center spokeswoman Danita Cohen said the Las Vegas hospital is taking in people with gunshot wounds. She didn’t have any more immediate information.
Zack, who said he was near the stage, told Fox News that his sister witnessed a concertgoer get shot in the head.
Country singer Jake Owen, tweeted, “Gun shots!!! Vegas. Pray to god. Love you guys. Love you Pearl.”
