CBS affiliate KLAS-TV reported that witnesses heard shots fired; video showed a police presence around the perimeter of the sprawling mall complex, and a helicopter circling overhead.
A Metro official said no one has been injured and that there are no reports of shots fired by the suspect.
Authorities in Las Vegas on Thursday said there was no threat to the public after an earlier massive police response at a mall after reports of a person with a gun.
Body Found During Search For Teenage Girl
Anyone with information on the case is urged to contact Lucan Garda Station at (01) 666 7300 or any Garda station. Gardai have found the body of 14-year-old Anastasia Kriegel in a disused farmhouse in Lucan, County Dublin.
At the time of the search, police said no person was located with a gun.
Police were still investigating the area late Thursday night with a tactical and K-9 team.
Boulevard mall manager Timo Kuusela said the incident started after reports that a man possibly carrying an assault weapon was spotted in the mall. "The mall has been evacuated while officers ensure the suspect is not inside", the spokesman says. "Police have not located this person and they are clearing the building to make sure the person is not hiding inside".