By Jericka Duncan and Tim Jimenez

LANSDOWNE, Pa. (CBS) – One woman is dead and more than three dozen people are displaced after an apartment fire Saturday morning in Lansdowne, Delaware County.

The flames broke out just before 5 a.m. on a third floor of the apartment building located at 32 Wycombe Avenue in Lansdowne.

“I turned to my brother and I woke him up and said ‘we gotta get out of here the whole buildings on fire,’ and I opened the door and there was smoke bellowing out, dumping out from the other door across the hall,” displaced resident Qron Lindsay said.

A few residents say Lansdowne Police officers were the first to respond. They started knocking on doors, getting people out. Several volunteer firefighters also responded.

Authorities say one woman was killed in the apartment where the fire started. She has been identified as 51-year-old Margaret McClernan. The Delaware County Medical Examiner has ruled the cause of death as smoke inhalation.

The building is a 24-unit apartment. At least 21 families were left without a home Saturday night because of the damage to the building.

“There’s extensive damage throughout the whole building because the third floor, the only way we could get to the fire spread was to pull the ceiling,” Lansdowne Fire Chief Wayne Worley said.

The Red Cross is assisting the displaced residents.

The cause of the fire is under investigation.