Chicago police said the crash happened at West Augusta Boulevard and North Long Avenue in the city's Austin neighborhood around 9:30 a.m.
A Toyota pickup truck was heading northbound on Long Avenue when it hit a Chicago Fire Department truck, which was traveling westbound on Augusta Boulevard, police said.
CFD said four people on their truck were taken to a local hospital. Their conditions were not immediately known.
The 32-year-old man who was driving the pickup truck was not injured. Police said he was cited for failing to yield to an emergency vehicle.
Authorities did not immediately provide further information about the crash.