Las Vegas Police Department advised people in a statement on Sunday night to stay away from Mandalay Bay Casino on the south end of the Vegas strip on Las Vegas Boulevard and across from McCarran International Airport.
Police said they gunned down one suspect but the shootout still continued.Police were also investigating reports of an active shooter in the city.
"Confirming that one suspect is down. This is an active investigation. Again, please do not head down to the Strip at this time," LVMPD said in a tweet.
Several people including a police officer had been shot at a nearby outdoor concert, according to the Las Vegas Sun newspaper. At least 14 of the injured were in critical condition.
Police also asked onlookers to avoid sharing "tactical positions" of its emergency officers on the internet out of fear that it would endanger the operation.
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One Twitter user claimed the hotel was on lockdown, while others, citing police scanners, said there were two shooters on the 32nd floor of the hotel who had shot at a bodyguard and police. Authorities were yetto confirm any of those details.
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Special SWAT units were deployed to the scene of the shooting. Police had shut down the strip.