Police have not yet identified the shooter and said that he died following a self-inflicted gunshot wound. The shooter had a rifle and a handgun on him, Brooks said.
Tulsa police said in a Facebook post just before 6 p.m. that the shooter was dead.
"Officers are currently going through every room in the building checking for additional threats," police said at the time. "We know there are multiple injuries, and potentially multiple casualties."
Tulsa police Capt. Richard Meulenberg said multiple people were wounded; he called it a "catastrophic scene."
St. Francis Health System locked down its campus Wednesday afternoon because of the situation at the Natalie Medical Building. The Natalie building houses an outpatient surgery center and a breast health center.
Aerial footage from a TV helicopter appeared to show first responders wheeling someone on a stretcher away from the hospital building.
A reunification center for families to find their loved ones was set up at a nearby high school.
Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives were also at the scene, a spokesperson said.