The fire started around 7:20 p.m. at the Ashwood Apartments located on the 700 block of Worth Boulevard in North Coventry Township.
Chopper 6 from sister station WPVI in Philadelphia was over the scene as heavy flames engulfed most of the three-story apartment building.
At least four people suffered non-life-threatening injuries.
Chester County officials said approximately 125 people have been displaced by the blaze. The Red Cross is providing shelter to 15 families.
According to witnesses, the fire started near the top floor of the structure and quickly spread along the roofline.
The apartment appears to have pre-dated firewalls, and crews had water pressure issues during the firefight.
Fire crews were dispatched from Delaware County to help with water supply issues.
On Friday morning, smoke was still rising from the charred remains of the apartment building.
The cause of the fire is under investigation.