More than 50 people were killed and 200 wounded when a gunman opened fire at a concert in Las Vegas on Sunday night, making it the deadliest mass shooting in US history. 

"We are looking at in excess of 50 individuals dead and of 200 individuals injured at this point," Las Vegas metro police sheriff Joseph Lombardo said after the shooting at a country music concert in the Nevada gambling hub. 

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Lombardo also told a press conference that the gunman, who was killed after armed police responded to the shooting, had been identified as a local man called Stephen Paddock, 64.

The police also believe that they have located his female companion, who had been earlier named as a person of interest.

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Dozens of patrol vehicles descended on the Strip after authorities received reports of an active shooter near the Route 91 Harvest Festival. Las Vegas police later said one suspect is "down" but did not give any other details. 

Concert-goers reported seeing muzzle flashes from the upper floors of the Mandalay Bay Hotel and Casino across Las Vegas Boulevard from the country music festival and the sound of what they described as automatic gunfire. 

Twenty six people have been admitted to the hospital, University Medical Center spokeswoman Danita Cohen said. Of those, 12 are in critical condition and the rest were being evaluated, she said. 

Witnesses said they saw multiple victims as they fled the gunfire raining down on the concert venue. Some later huddled in the basement of the nearby Tropicana hotel-casino. 

Some officers took cover behind their vehicles while others carrying assault rifles ran into the Mandalay Bay Hotel and Casino. The authorities shut down part of the Las Vegas Strip and Interstate 15. 

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Witnesses say country singer Jason Aldean was playing near the end of the concert when the gunfire began. Some flights destined for the McCarran International Airport were diverted due to the shooting. 

(With agency inputs)