AT least 58 people including off-duty police officers have been killed and more than 100 other people injured in a mass shooting at an outdoor music festival on the Las Vegas Strip, officials said.

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 killed a suspect on 32nd floor of a hotel across from the concert, and said they did not believe there were any other attackers.

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.

Northern Echo Sports Editor, Nick Loughlin, who is holidaying in Las Vegas, said: "We are staying in the Wynn Encore, it's about two miles from the scene. 

"We heard some sirens earlier on while heading back but it seems there was no panic or word of anything happening at our end of the strip. 

"We did go past the Mandalay Bay earlier this afternoon and went by the festival site too where the shootings happened. 

"It's very close to the "Welcome to Vegas" sign and the airport - we are due to fly home tomorrow night. 

"There's been no advice from our hotel about what to do and we are just watching it unfold on NBC from our hotel room."

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.