The suspected lone shooter was also dead.
Louisville Metro Police Department said a gunman was “neutralized” following the incident inside Old National Bank about 8.30am on Monday morning.
Deputy Chief Paul Humphrey told reporters officers who arrived on the scene “encountered active gunshots still being fired inside the location at that time.”
Officers exchanged gunfire with the shooter, who appeared to be a former employee of the bank, but it wasn’t clear how he died.
Police deploy at the scene of a mass shooting in Louisville, Kentucky
In a tweet, Kentucky Governor Andy Beshear said he was heading to the scene.
“Please pray for all of the families impacted and for the city of Louisville,” Mr Beshear said.
The FBI said its agents were also responding to the shooting not far from the Louisville Slugger Field and Waterfront Park.