A 64-year-old man armed with more than 10 rifles fired on crowds at a country music festival from an overlooking hotel, killing at least 58 people, and injuring more than 500.
Police confirmed in a tweet one suspect was down and said it was an active investigation. They later tweeted that they did not believe there were any more shooters.
Las Vegas Police Sheriff Joe Lombardo said they had found the shooter on the 32nd floor. He has been named as Stephen Paddock, 64, who lived in a retirement community in Mesquite, Nevada.
"Approximately 10.08pm tonight, this evening, we had calls come into dispatch of multiple shots being fired in the direction of the Mandalay Bay towards the Route 91 concert that was taking place on the east side of the Las Vegas Boulevard."
"We believe he is the sole aggressor and the scene is static at this point."
Paddock killed himself before police entered the hotel room he was firing from, Mr Lombardo told reporters.
Mr Lombardo told media that police had located the shooter's travelling companion, a 4'11'' (1.49m) woman named Marilou Danley, who they had been looking for. They had also found the two vehicles they had been looking for.
He said the FBI was helping with the investigation and Clark County Fire was helping with the victims.
He said reports of multiple shooters or blasts in other locations had been proven false.
Police officers were among those who had been shot.
"I have two police officers that are in hospital - one in critical condition and the other one minor injuries - but there are other police officers that were off duty that were attending the concert that have expired.
"We do not have those individuals identified at this point."
Witnesses said a shooter began firing down into the crowd with an automatic weapon at the Route 91 Country Music festival, which was taking place just across the road from the hotel.
'The shots just kept coming ... and we ran, and everybody's hiding'
One woman told CNN and Reuters she was caught up in the shootings.
"The shots just kept coming and so we were going down and when we got down there was a man that was shot right there.
"They were trying to take him out, he was all bloody, he was unconscious and one of my friends was helping him out and they got him out.
"And we ran, and everybody's hiding everywhere, I mean they're hiding under the bleachers and the stanchions and everywhere they could and everybody's telling us to run, run as fast as you can.
A Canadian man in Las Vegas for a conference, Todd Price, said it was a terrifying experience.
"We heard three or four shots and then what sounded like rapid machine gun fire in four or five bursts.
"We went into the hotel and then they started shutting down the casinos and moving people out at that point in time and we tried to get into our rooms and they shut down the elevators and started escorting everybody out."
One Twitter user posted that the hotel was on lockdown, while another, citing police scanners, posted there were two shooters on the 32nd floor of the hotel who had shot at a bodyguard and police.
Shooting in Las Vegas. People fleeing (video from the Mandalay Bay hotel) pic.twitter.com/hs98J5uK6T— Eiki Hrafnsson (@EirikurH) October 2, 2017
Las Vegas' McCarran International Airport tweeted that flights had been temporarily halted because of the reports of shootings. Limited flight activity restarted about two hours later.
Videos on social media showed hundreds of people fleeing from the scene. The sound of what appears to be automatic gunfire can be heard in some clips.
- RNZ / Reuters / BBC