It happened just before 3 p.m. on the 4400 block of North Broad Street.
Police say a three-story apartment building caught fire and the flames spread to three homes on Cayuga Street.
One firefighter was hospitalized for burn injuries to his hand.
Nobody else was hurt, police said.
Roughly 20 to 25 people are displaced at this time.
The cause of the fire is still under investigation.