A First Student school bus and three other cars were involved in an accident at Stadium Boulevard and Broadway at about 3:50 p.m. on Friday.
No students were on the bus at the time of the accident, said Bill Lehman, contract manager with the bus company.
One person was bleeding from the head, and at least two people were taken to the hospital.
Menghistab Siele, who witnessed the crash as it happened behind his car, said he saw the school bus run into the car in front of it. That car then collided with two cars in front of it, causing a pileup.
A father and son who were in the car hit by the bus were taken away in an ambulance, Siele said.
Missourian reporters Naomi Weisbrook and Julia Haslanger contributed to this story.