No other people were injured in the violence, which erupted about 2 p.m.
(2000 GMT) at the sprawling campus of more than 20 buildings, where more than 1,000 workers are employed by the beer company in Wisconsin's largest city, according to the police chief.
"There is no threat at this time, and we will continue to investigate throughout the night," Morales told reporters at a news conference hours after the shooting.
Morales said the bloodshed was confined to the Molson Coors facility, and that "no members of the general public were involved." The suspect was described only as a 51-year-old Milwaukee man.
Details about the circumstances of the shooting, including what may have precipitated the carnage, were not provided by authorities.