More than 50 people have been killed and more than 500 wounded during a shooting at an outdoor country music festival on the Las Vegas Strip Tuesday night (late Sunday US time).

Dozens of patrol vehicles descended on the Strip after authorities received reports of an active shooter near the Route 91 Harvest Festival.

Police confirmed at a press conference that the suspect, a local man, had been killed by police. They later named him as 64-year-old Stephen Paddock.

According to Mesquite police, Paddock lived in a retirement community, with no prior run-ins with law enforcement.

They said he had a female companion they wanted to speak to and identified her as Marilou Danley. They later said they were reasonably confident "but not 100% sure" that she had been found.

The death toll from a lone gunman is over 20 with over 100 people injured. Video / AP

Police said they believed it was the actions of a "sole aggressor" on the 32nd floor of Mandalay Bay Resort and Casino.

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Police said they did not yet know what the shooter's belief system was.

Reports of more shooters and explosions were false, they said.

Concertgoers reported seeing muzzle flashes from the upper floors of the Mandalay Bay Hotel and Casino across Las Vegas Boulevard from the country music festival and the sound of what they described as automatic gun fire.

Concertgoers reported they heard what initially sounded like fireworks. The music stopped temporarily and 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.

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.

Some flights destined for the McCarran International Airport were diverted due to the shooting.

A spokesman for New Zealand's Ministry of Foreign Affairs and Trade said MFAT was responding to the reports.

He said there were 44 New Zealanders registered on SafeTravel as being in Las Vegas and 2157 in the USA.

"The New Zealand Consulate-General is in contact with the local authorities. There are no indications at this stage that any New Zealanders have been caught up in the incident," he said.

"Any New Zealanders in the vicinity are advised to stay indoors, follow any instructions issued by the local authorities and let their family in New Zealand know they're okay.

"New Zealanders who require consular assistance are advised to contact the New Zealand Consulate-General in Los Angeles: +1 310 566 6555."

- Additional reporting by Associated Press.