The fire caused $50,000 in damage, said Capt. Chad Deardorff of York City Fire/Rescue Services.
A state police fire marshal was unable to determine the cause of the fire, he added.
Eight adults and 10 children were displaced by a three-alarm fire Saturday afternoon in York.
Crews were dispatched at 3:49 p.m. to the 700 block of West Princess Street, where firefighters saw smoke pouring from several rowhouses, said acting York City Fire Chief David Michaels.
The fire was knocked down by 4:30, and damage was contained to four properties, Michaels said. One of the homes was being renovated, and damage to the eastern-most home was minor.
A volunteer York City firefighter suffered what appears to be a heat-related injury, Michaels said, but no one else was harmed.
The Red Cross is assisting the families displaced by the blaze.
On a warm day like Saturday, heat becomes a significant obstacle, the chief said. Groups of firefighters are rotated in and out of affected properties to make sure no one becomes overheated or dehydrated.
As many as 75 firefighters from York City and surrounding fire departments assisted at the scene, Michaels said.
A state police fire marshal is investigating.