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Witnesses have described seeing people fall dead in front of them as a gunman fired "clip after clip" into a crowd of around 30,000 at an outdoor country music festival in Las Vegas.
At least 50 people have been killed and more than 200 injured by gunman Stephen Paddock who fired from the 32nd floor of the Mandalay Bay hotel, picking off revellers before he was shot dead by police.
"They were firing from somewhere high, and they were unloading clip after clip after clip after clip," one witness told local station, KSNV News.
"It was hundreds of shots ... There were bullets flying everywhere. Everybody was running. It was really, really bad."
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A local woman said the shooter seemed to follow groups of people as they ran to try to find cover.
"They started shooting and people started dropping around us .... there are a lot of dead bodies," she told local TV.
Another said a woman standing next to her was shot.
"I heard what we thought was firecrackers, and we looked to the right of us and there was a woman down covered in blood," the witness, identified as Emily, told local TV station KLAS.
"From that point on we just ran. We hid wherever we could, and now in an airplane hangar.
"We had no idea, it was just rapid fire. We all thought we were dead. It was awful. It just kept going, and going and going.
"It felt like an eternity but it went for at least several minutes.
"Each place we hid for a couple of minutes, and we moved to a new location and the fire would start again."
Concertgoer Ivetta Saldana said she hid in a sewer.
"It was a horror show," she told the Las Vegas Review-Journal.
"People were standing around, then they hit the floor."
An Australian man believed the gunman was staying the room next to him at the Manadalay Bay hotel.
"It was hardcore, like it was full machineguns for 20 seconds and then it stopped for five seconds then it just went again it," Brian Hodge told Fairfax Media.
"There were so many shots fired, I couldn't tell you many. A woman came right up to my face and she said "you've got to turn back there is a shooter" and we all just started running."
A NSW family caught up in the tragedy said they experienced the "scariest night of our life" and had to walk with their hands up across an empty casino.
Kevin Comerford, Nicole Shipman and her daughter Maddy Aspinall, 14, from Grafton in NSW, were in Las Vegas for one night only after a dance academy tour in the US had finished.
"This was supposed to be a one night special stop because we'd never been to Las Vegas before ... we were planning to live it up for one night and we've had probably the scariest night of our life," Mr Comerford told AAP on the phone.
Channel Seven journalist Ashlee Mullany said the noise "sounded too loud to be a gun".
"I felt sick to my stomach knowing that those hundreds of rounds that I heard were bullets raining down on those people that were just there enjoying a music festival," she told Sunrise.
It's not know whether any Australians were hurt in the attack.
"If you have any concerns for the welfare of family and friends in the Las Vegas area, you should attempt to contact them directly," a Department of Foreign Affairs and Trade spokeswoman told AAP.
People unable to make contact with loved ones should phone the DFAT emergency hotline: 1300 555 135, or +61 2 6261 3305.
Las Vegas Mayor Carolyn Goodman described the city as a "safe place" for tourists and called Paddock "a crazed lunatic full of hate".
