Residents described a chaotic scene as smoke filled hallways and people panicked, with several trapped on balconies waiting for rescue.
"We just ran back to one of our neighbor's apartments, we closed the door, and we went to the deck," said Raymond Erwin, a resident.
Erwin said he was among those rescued from a balcony around 10:30 a.m.
"They got us down with the ladders, it was definitely very scary," he said.
Fire crews from multiple departments responded to the three-story building and worked to knock down flames that started on the second floor.
Officials said one resident later died at the hospital, another remains in critical condition, and six others were treated for non-life-threatening injuries.
"Fires in apartment buildings are exceptionally challenging when the fire is anywhere below the top floor. You have all of the floors above to deal with. So in this case you have people trapped on the second floor, you have people trapped on the third floor," said Nick Martin, fire chief for Upper Darby Township.
One firefighter suffered burn injuries and was hospitalized but has since been released and is recovering.
The fire caused extensive damage, with smoke affecting apartments on the second and third floors and water damage on the first floor.
Delaware County Emergency Services, the Red Cross, and other support groups assisted displaced residents.
A reception center was set up at Drexel Hill Middle School before the apartment complex property manager secured temporary housing. "
It's definitely a little traumatizing, very scary, honestly I'm still trying to process it," Erwin said.
Firefighters said the flames were contained to one apartment. The cause of the fire remains under investigation.