At least two people are dead and 24 have been injured in a mass shooting at a country music festival in Las Vegas, a hospital spokesman says.
Dozens of patrol vehicles descended on the strip after authorities received reports of an active shooter near the Mandalay Bay Hotel and Casino.
Witnesses say they saw multiple victims as they fled the gunfire raining down on the concert venue.
University Medical Centre spokeswoman Danita Cohen said the Las Vegas hospital is taking in "several" people with gunshot wounds.
One Twitter user posted that the hotel was on lockdown, while another, citing police scanners, said two gunmen who had shot at a bodyguard and police were on the 32nd floor of the hotel.
Witnesses heard numerous gunshots at the hotel, where police tactical teams were searching for the attacker, according to reports on CNN and in the New York Times.
The Las Vegas Police department say one suspect is down and they do not believe there are any more shooters.
Videos showing concert-goers taking cover and running for cover are flooding social media, with terrifying gunshots heard in the background.
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Some police officers took cover behind their vehicles while others carrying assault rifles ran into the hotel.
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.