Crews worked for several hours before getting the blaze under control around 9 p.m. Friday.
Fourteen people were displaced and dozens of others were evacuated from nearby buildings.
Fire victim Diana Ruzat lived on the third floor of the apartment building on Sharon Avenue, and says she lost everything.
"Left to walk my dog and my boyfriend hears a pop pop pop! He's like, there's smoke coming from your apartment! I ran as fast as I could," She said.
Crews responded to reports of an explosion at the back of the building around 2:30 p.m.
One resident was taken to the hospital for smoke inhalation.
Flames shot from the roof and thick smoke flooded the area.
3 alarms. 1 injury. Still putting water on it. pic.twitter.com/dP9nWrCTRT— Trish Hartman (@TrishHartman) August 25, 2017
Vera Cameron of Sharon Hill said, "When I came out, the only thing you could see was all this black smoke. So you couldn't come through, you had to take the long way around."
Chris Bailey of Raleigh, NC was visiting his mom.
"The whole neighborhood. It was like a smoke bomb went off. You couldn't see anything," he said.
Angela Costa lived on the third floor too. She was at work when the fire started and her two cats - Tigger and Alexander - are presumed dead.
She said, "I hope they didn't suffer much. I hope they went quick if they're going to go."
Six apartments made up the three story building. Crews used a drone to get an aerial view of the fire. Officials say it's the first time they've used the county-owned drone to help fight a fire.
Sharon Hill Police Chief Richard Herron said, "I'm sure you've seen they've been back here a lot looking at this. It gives them a whole aerial overview of how much damage is in there actually."
As the blaze continued to burn into the night, an excavator started tearing down walls to give firefighters better access to the flames.
The American Red Cross is helping all of the residents, who now have to find a new place to live.
"I guess it'll be a whole new fresh start," Costa said.
Firefighters began tearing down the building, once the blaze was under control.
There is no word yet on a cause.
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