The shooting took place at the Mayfield Mall in Wauwatosa, a Milwaukee suburb of 47,000 people. Another woman said a friend who works inside the mall was hiding in a stockroom after shots rang out.
Wauwatosa Mayor Dennis McBride said in a statement that none of the injuries appear to be life-threatening.
Video posted to Twitter showed paramedics wheeling people out of the mall on stretchers.
One witness claims she heard "8 to 12 shots being fired".
Wooley said she didn't see anyone but the shots were "very close". She added that they ran in the opposite direction to the basement of the store, where they then hid.
A man said his daughter called him from inside the mall, during which he heard gunshots over the phone and what sounded like people running for cover.
An agent who wouldn't give his name said the mall was being "methodically" cleared.
A large number of emergency services, including the Federal Bureau of Investigation and heavily-armed police officers, responded to the scene.
"We are disheartened and angered that our guests and tenants were subject to this violent incident today", Brookfield Properties, Mayfair's Mall property management company, said in a statement.
"Police are actively investigating an incident at Mayfair Mall", Wauwatosa police said in a tweet.
The mall was the site of a February shooting in which Alvin Cole, a black male 17-year-old, fired a stolen handgun at Officer Joseph Mensah, which subsequently turned into months of turmoil for the officer, resulting in his resignation this week, even though the shooting, along with two others during his career, were justified, Law Officer reported. The Milwaukee County District Attorney's office cleared Mensah in the shooting.