Two firefighters were injured while battling the blaze on North 14th Street, including one who fell down a flight of stairs and the other who suffered an electric shock, the Whitehall Township Bureau of Fire said.
The first firefighter was taken to a nearby hospital and later released, while the second was treated on the scene, local officials said.
"Upon arrival, there was heavy fire in the one apartment with the fire spreading to the common attic," the bureau said. "A trench cut was used in the roof to release the heat and smoke."
The Red Cross was helping the displaced families, officials said. They added that pets were also lost in the blaze.
The cause of the fire remains under investigation.
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