Esker employee Gabe Geib says he heard a couple of shots but didn't immediately know what it was. He said he then saw people running "full sprint" away from the building.
One local resident shared a video of police cars racing to the scene of the shooting, which reportedly happened around 11:30am EST, with local news outlets announcing that a cordon has been set up.
Keely Arthur of CNN affiliate WISC said about 50 police cars and the Federal Bureau of Investigation are at the scene. WSAW reports that at around 10 a.m.an automated message played in another office in the building telling employees there to take cover. There are 34 stores and restaurants in the center that were temporarily closed, Kautzky said.
The Middleton police department sent out an alert stating: "ACTIVE SHOOTER: 1800 Deming Way Officers and emergency personnel are on the scene on an active shooter in the 1800 block of Deming Way in the City of Middleton".
Witnesses said a man had walked into a software company and opened fire, injuring multiple people.
Police and multiple ambulances have responded.
Middleton Police are leading the investigation. She provided no additional information.