BOULDER, Colo. (AP) — Investigators are trying to determine what caused a fire that killed a 57-year-old woman in northern Colorado.

Firefighters with the Boulder Rural Fire Protection District were called to the condominium blaze in Gunbarrel late Friday night. Neighbors had rescued the woman and her 19-year-old daughter, but The Boulder Daily Camera reports the elder woman died after collapsing outside. Her name has not been released.

Investigators say it's hard to tell how and where the fire started because the flames flashed through the apartment when the door was opened, scouring all of the initial fire patterns inside of the condo. They do not suspect foul play.

The woman's daughter was not injured.