It began on Sunday night, when young people gathered on the street near Pulaski and Iowa in Humboldt Park.
Video shows hundreds of people swarm a Shell gas station nearby.
Employees said they locked the doors because of the sheer masses.
As the crowd continued to grow, gunfire broke out around 12:46 a.m., according to police.
Surveillance video shows people ducking behind cars to avoid the gunfire.
At least one other person at the gathering did have a gun.
The youngest victim was a 15-year-old girl who was shot in the neck and taken to an area hospital in serious condition, police said.
"People are trying to figure out which hospital their friends and loved ones had gone, there were ambulances everywhere," Crisis Responder Pastor Donovan Price said.
An 18-year-old woman was shot in the back; a 19-year-old woman was shot in the arm; a 25-year-old man had gunshot wounds to the buttocks; a 35-year-old man was shot in the foot, all were taken to the hospital and listed in fair condition, police said.
Price described the chaotic scene saying that people's belongings flew everywhere in sheer panic.
A 33-year-old woman broke an ankle in the chaos, and was taken to an area hospital for treatment.
A gas station employee said they called police for help seven times; adding that it's common for young people to gather in the area on weekends.
On Monday alone, at least 24 people were shot, two fatally, according to Chicago police.
Seven people were also shot near 60th and Winchester in West Englewood.
Those victims were also in their 20s and 30s.
READ ALSO | 7 injured, 1 critically, in West Englewood shooting: Chicago police
At least 71 people were shot, nine fatally, in gun violence across Chicago from Friday evening to Monday morning, CPD said.
No one is in custody in either of these mass shootings. CPD area detectives continue their investigation.
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