The male teenagers -- 17 and 18 years old -- were shot less than a block from a bus stop at 75th Street and Constance Avenue around 2:50 p.m.
One was hit in the back and the other in the leg. They were both taken to local hospitals in serious to critical condition. One is at Northwestern Memorial Hospital and the other is at Advocate Christ Medical Center.
Police said one of the shooting victim flagged down westbound No. 75 bus after being shot. The driver stopped and called for help.
A group of students was waiting at the stop when the gunman approached and fired several shots, hitting one male student in the back and another in the leg.
Police said there may have been a number of witnesses because South Shore High School, 7529 S. Constance, had just let out. Also they will look at cameras in the area. A blue light camera is posted directly across the street.
"We're looking at all possibilities and also we're just going to meet tomorrow morning with the public schools, Chicago Police Department, as we find out more," said Commander Christopher Fletcher, Chicago Police Department.
Emanuel Hall says he was on the bus and watched as the gunman fired what he thought were about five shots.
"I know everybody had to know who he was. There was no argument going on at that point," said Hall.
Both teenagers are students at South Shore, according to Chicago Public Schools. They are in stable condition.