Authorities say the fire broke out shortly before 1:30 p.m. at South 20th and Ferdinand streets, about two miles west of the downtown area.
Hot weather and low water pressure hampered the firefighting effort.
Two buildings burned to the ground, and five nearby homes were damaged.
Fire department spokesman John Brown said about a dozen firefighters, working in 90-degree temperatures, were treated for heat-related injuries.
There were no reports of injuries among residents.
At least six families, about 19 people, are now displaced.
Three of the buildings were six-family homes, and the other four were two-family homes. Two of them were vacant.
The cause of the fire is under investigation.
The Red Cross is providing shelter to the displaced families.