The fire broke out around midnight on the unit block of S. Jefferson Street in Lehigh County.
When crews arrived, flames showed from multiple homes after spreading to neighboring houses.
The blaze was quickly upgraded to a four-alarm fire and took over an hour to get under control, according to fire officials. Six separate departments responded to help.
At least 33 people have been displaced.
One firefighter was injured from battling the blaze and taken to the hospital, authorities say. There is no word yet on the firefighter's condition.
A North Penn Goodwill Service food truck was at the scene providing food and drinks to people and firefighters. The Red Cross was also there to assisst.
There has been no word on the cause of the fire or if there were any other injuries.