Witnesses told the Associated Press that they could see muzzle flashes coming from the Mandalay Bay Hotel and Casino's high floors and described the sound of automatic gunfire. Police said they confronted the gunman on the hotel's 32nd floor. Police said the gunman was a local resident but did not identify him.
The shooting appeared to take place near the Route 91 Harvest Festival, a three-day country music concert held over the weekend that reportedly drew 30,000 attendees. The concert grounds are adjacent to Mandalay Bay. The shots began as Jason Aldean, one of the final performers, was playing.
One witness, Ivetta Saldana, told the Las Vegas Review-Journal that Aldean was rushed off stage when the shots rang out. "It was a horror show," she said. "People were standing around, then they hit the floor."
Videos posted to Twitter from people claiming to be witnesses showed people screaming and running for cover amid the sound of gunshots. The shooting continued intermittently for more than five minutes, according to the Associated Press.
"The gunfire never ended, it seemed like," concert attendee Rachel Dekerf told CNN. "It just went on and on and on."
Police converged on the area and blocked off roads. Some officers could be seen taking cover behind squad cars as other officers ran into the casino, the Associated Press reported.
Some of those with gunshot wounds were taken to University Medical Center, a spokeswoman told the Associated Press. Police urged everyone to avoid the south end of the Strip.
One of the victims was an officer with the Bakersfield Police Department in Southern California, according to a statement from the department. Several of the department's officers were off-duty and attending the concert when the gunfire erupted. One of them was struck by a bullet and was taken to a local hospital for non-life-threatening injuries, police said. His name was not released.
"I understand the people of Las Vegas want to help," Sgt Jeff Clark said in a news briefing early Monday. "I see a lot of people out here that are coming down wanting to help. Please, steer clear of the area ... Please, stay away from the area."
Multiple flights bound for the McCarran International Airport were diverted because of the shooting, the airport tweeted. All other planes were temporarily grounded, with a few flights resuming Monday morning.
The Route 91 Harvest Festival has been held for the past four years on a 15-acre lot across an intersection from Mandalay Bay. The concert's main stage is situated near the northeastern side of the gold-colored hotel-casino, which towers more than 400 feet above the Strip.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)