People inside the building were ordered to shelter in place, initial reports said.
There were early conflicting reports on the number of casualties and the number of potential shooters.
Several accounts put the number of people shot between five and eight.
At least one witness reported shots going off near a Bath & Bodyworks store inside the mall. At least eight to 12 shots were fired, according to early reports.
Police and emergency vehicles flooded the scene outside, and a police SWAT vehicle was reportedly en route.
Three ambulances were seen departing the scene with several victims.
The Milwaukee bureau of the FBI has reportedly sent a tactical response team to investigate.
This is a breaking news story. Please stay with AJC.com for the latest updates.