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.
Paddock's girlfriend, who was outside of America at the time of the shooting, has been located and identified as Australian woman Marilou Danley, who moved to the US from Queensland over a decade ago.
After sending out a request for her whereabouts, the Las Vegas Metropolitan Police Department said in a statement that "detectives have made contact with her and do not believe she is involved with the shooting on the strip," SMH reports.
Paddock's niece Nicole took to Facebook to address the attack and her family's shock at their relatives' actions. "First off I want to express my deepest sympathies to everyone affected by this massacre, I am as shocked and appalled as anyone about this senseless act of violence," she wrote.
"It has been especially disheartening to find out that the perpetrator is a relative. Stephen Paddock was my uncle, but I did not know very much about him. Sometimes I would see him in Las Vegas when I was there visiting other family, but these encounters were casual and infrequent," she continued. "It has been well over a year since I have had any contact with him. I cannot speak to what possibly motivates someone to do something like this nor what his specific motivations may have been. He never came across as religious or political."
"My family and I are still in shock by this news and my heart goes out to all of those who lost or had loved ones injured in this tragedy. I am at a loss for words."
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.