The shooting happened in the Brighton Park neighborhood's 4300-block of South Kedzie Avenue at about 4 a.m. on Sunday, police said.
One man shared video with ABC7 showing spectators and participants taking over the streets and driving recklessly. The man said it was all fun and games until just a few minutes later.
Video shows reckless street stunts moments before a deadly shooting in Brighton Park
"I'm out and I went on the corner," witness Darrell Cross said. "I'm watching and having fun and all of a sudden, I see a white van come out of the valley over there and they just open fire."
Police said the shooting occurred as officers were responding.
"Approximately 100 cars had gained control of an intersection," CPD Commander Don Jerome said. "As the officers were responding, we received a ShotSpotter alert of at least 13 rounds."
WATCH: CPD provides update after 5 shot, 3 killed amid street drifting
CPD provides update after 5 shot, 3 killed amid street drifting
Over the summer, the city passed an ordinance to crack down on illegal drag racing and drifting. It could result in towing the vehicle and a fine up to $10,000.
Alderman Ray Lopez said it's not working.
"This phenomenon, which probably started out as boredom, has now become a mainstream, circuit-style event," Alderman Lopez said. "It's being promoted on social media. It's being encouraged."
Police said all three of those killed had gang affiliations and that caravan was just one of several reported citywide Sunday morning.
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Police did not recover any guns on the scene and said they are still looking to speak with "one or two people" who are "not necessarily" those in the hospital.
No arrests have been made and Area One detectives are investigating.