The 64-year-old gunman, who police have identified as Stephen Paddock, armed himself with more than 10 rifles before shooting at the crowd from the window of the nearby Mandalay Bay hotel, 7 News reports.
Paddock had no police record or history of violence and reportedly killed himself as police stormed his hotel room.
An Australian family from Grafton, NSW were visiting Las Vegas for the first time on the night of the shooting.
Kevin Comerford, Nicole Shipman and her daughter Maddy Aspinall, 14, were walking around the city, two blocks away from the scene, when they saw terrified people running towards them.
"This was supposed to be a one night special stop because we'd never been to Las Vegas before," Mr Comerford told AAP.
"We were planning to live it up for one night and we've had probably the scariest night of our life."
He said that teenager Maddy handled the incident well until they were made to walk through the empty casino with their hands above their heads.
"It became very, very real for her then," he said. "That's when she got very upset. She's been a brave girl."
Another Australian, Brian Hodge from the Gold Coast, was staying in the hotel room right beside the gunman.
"It was a machine gun from the room next to me," he told News Corp.
"My floor is a crime scene. They killed a security guard on my floor."
Hodge said he fled the hotel during the chaos and hid in the bushes for "several hours" waiting for police.
People unable to make contact with loved ones in Las Vegas should phone the DFAT emergency hotline: 1300 555 135 or +61 2 6261 3305.
