Mayor Tom Barrett told reporters that several people, including the shooter, have died.
“It’s a horrible, horrible day for the employees here,” Barrett said. “It’s a very rough day for anybody who’s close to this situation.”
Several local news outlets have reported fatalities, but CNN has not confirmed a specific number.
Earlier on Wednesday, Milwaukee police said they were investigating a “critical incident” in the area near the 4000 block of W. State Street and asked the public to stay away from the area. Police have since said there’s no active threat at the complex.
Police have released few details. A news conference was planned for 6 p.m. (7p ET).
US Sen. Tammy Baldwin of Wisconsin described the incident as a mass shooting.
‘Find a safe place,’ texts warned employees
“Find a safe place, active shooter on campus,” said one of the text messages shared with WITI.
Another employee, who was not at work at the time of the shooting, told CNN they began receiving texts and email communications about 2:18 p.m. (local time).
The first text indicated there was an active shooter in or near “South Packaging, building 4 2nd floor stairwell.”
Multiple local and federal law enforcement agencies, including the Bureau of Alcohol, Tobacco, Firearms and Explosives, responded to the scene.
FBI Milwaukee is supporting police in the “very active scene,” spokesman Leonard Peace said.
The CEO of Molson Coors is heading back to Milwaukee from a company conference that was taking place in Texas, according to a source familiar with the company.
CEO Gavin Hattersley was at the conference when he suddenly announced he was departing.
This is a developing story. Return for updates
CNN’s Eric Levenson, Paul Murphy and Brynn Gingras contributed to this report.