There were Chicago police officers inside the mall, but witnesses say they were simply outnumbered.
Signs were thrown, vehicles were damaged in the parking lot, as many as 20 people were arrested and two people were treated for minor injuries.
A video posted on YouTube shows a fight outside Ford City Mall, just part of the chaos that ensued.
"It's like a mob scene, just jumping on cars, breaking windows," said witness Moses Khativ.
It all began around 4:45 p.m. Saturday after a large crowd had gathered at Ford City Mall for an autograph session by the music group Mindless Behavior.
The event had wrapped up when mall officials say a group of about 30 young people began causing trouble.
"They started jumping on these couches that we have inside the mall, and security told them to calm down and they didn't," said mall employee Jasmine Murillo.
Murillo was working at one of the stores and quickly lowered the security gate after a fight broke out.
Soon, more than 100 people, she says, were running through the mall.
"I left my sign outside the door where it has a logo and everything," she said. "And they picked that up and threw it at people. They were throwing it at security, police, kids, anything. Anything they found, they picked up and started throwing."
"It was like crazy," said witness Lexus Finley. "And then kids just started going crazy. There was like gang members there."
As the mall was shut down, witnesses say the crowd spilled outside with large groups roaming the parking lot.
"They jumped on top of cars," said a witness identified as Robert. "They stopped traffic. They busted a lady's windshield in the back of her car. They knocked the rearview mirrors off."
The Chicago Fire Department says at least two people were taken to hospitals with minor injuries, including a CTA bus driver who was hit by a thrown object.
"They were throwing snow at the police. Anything you can think of, they were doing that," Robert said.
The crowd would end up crossing busy Cicero Avenue and targeting other businesses at another mall, including a Best Buy store.
"It's horrible," Murillo said. "It's like young kids, you get an opportunity to meet one of your favorite stars, and look at how you react to that."
Officials say there were no reports of theft at any of the stores.
At least a dozen people were taken into police custody.
Ford City Mall was expected to reopen Sunday at 11 a.m.
