Several people were killed Wednesday when a sacked former employee opened fire at the Milwaukee campus of brewing giant Molson Coors, with reports of up to six dead in addition to the shooter.
"There are multiple fatalities... I believe including the shooter," Milwaukee mayor Tom Barrett told reporters after visiting the scene.
"It's a horrible, horrible day for the employees," he said, urging residents to stay away from the area.
US media including ABC News and the local Fox affiliate reported the shooter had been fired earlier in the day from the beer giant, which owns the Coors and Miller brands.
The local CBS affiliate said the shooter appeared to have stolen the nametag of another employee before returning to the office complex with a gun.
The Milwaukee Journal Sentinel said six people were killed in the rampage, in addition to the shooter. The local CBS affiliate said four people were killed as well as the shooter.
Police in the Midwestern city were to hold a press conference at 6 pm CST (0000 GMT).
They tweeted that the scene remained "active" -- but that there was no longer an "active threat." The Chicago division of the Bureau of Alcohol, Tobacco, Firearms and Explosives was also on site.
Molson Coors said it was working with the police department, adding: "Our top priority is our employees."
The Journal Sentinel earlier quoted the husband of a brewery employee, Lasonya Ragdales, as saying she was informed by the company of an active shooter on the premises, and was texting him while locked in a room with co-workers.
Nearby schools were also placed on lockdown.
Known until last year as MillerCoors, the beer company announced in October 2019 that it would undergo a large restructuring and officially changed its name to Molson Coors Brewing Co.
It also moved its North American headquarters office from Denver to Chicago and shifted hundreds of corporate office jobs to Milwaukee. The company was expected to cut 400 to 500 jobs throughout the organization during the restructuring.
In a statement, UAW union president Rory Gamble called the incident "shocking" and extended "deepest sympathies" to the families of the victims.
"We do not yet know what led to today's incident. But we do know that deep down we must work to ensure that every person that goes to work in the morning will come home safe to their family in the evening," he said.
"We will continue to advocate for safety, mental health services, and common sense gun provisions in the workplace." The Milwaukee shooting is the latest in a long list of gun-related violence in the US, which saw a record 417 mass shootings in 2019, according to the research group Gun Violence Archive.