People fled the Bellagio casino in Las Vegas as a suspected robber wearing a pig mask sparked fears of a shooting.
The casino and hotel was put on lockdown as reports of an "active shooter" circulated.
Police later called those reports "false", but acknowledged at least one of three suspected thieves had fired shots.
Tyler Perkins said he was stood outside the complex when "hundreds start pouring out the door".
NinoNJ said he had to "run to escape",
"Bellagio store appears to have been robbed by masked individuals with sledge hammers," he wrote on Twitter.
Kir_kamil said on Twitter: "Literally just witnessed an armed robber in a pig mask at a Rolex store at the Bellagio & then his arrest."
Police confirmed one person was arrested and added there were no injuries.
Parts of the casino complex remain closed while police investigate.