Las Vegas police tweeted late Sunday that officers were responding to reports of an active shooter near the famous casino.
A University Medical Center spokesman told Reuters that there were at least two dead and 24 injured.
Police asked people to avoid the area.
The Route 91 Harvest Festival was taking place on the Vegas Strip. The gunfire was rapid and reportedly at first confused with firecrackers.
“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.
Country music star Jason Aldean was reportedly performing when the gunfire erupted.
There was a massive police response. One witness told KSVN that he heard “hundreds of shots.”
Zack, who said he was near the stage, told Fox News that his sister witnessed a concertgoer get shot in the head.
The station reported that there were multiple victims. The area is now on lockdown. All clubs and businesses on the strip are closed.
Country singer Jake Owen, tweeted, "Gun shots!!! Vegas. Pray to god. Love you guys. Love you Pearl.
University Medical Center spokeswoman Danita Cohen said the Las Vegas hospital is taking in "several" people with gunshot wounds. She didn't have any more immediate information.
UPDATE:
One suspect is "down," police said. Police do not believe there was another shooter.
Story From FoxNews.com