A woman who called 911 about a fire in her Fort McMurray apartment building says warnings didn't go off when she pulled the building's alarm system.

"It was sickening," Lindsay Johnston said through tears on Tuesday. "It was just a feeling of absolute helplessness and just all we kept thinking was, are people even going to get out alive."

Johnston and her boyfriend Richard Bookel first noticed the fire in the 160-unit Parsons Landing apartment around 11:30 p.m. Sunday.

"Appeared to be fire coming from the apartment window, all the way up," Bookel said. "Two or three floors it had already reached. Definitely fire within the building as well, at that point, and there was no fire alarm going off."

Johnston called 911 and was instructed to pull the alarm on the wall. Magnetic doors in the hallway closed, but no alarms or sprinklers went off.

"We went down the stairwell, we could faintly hear just a slow, periodic "bah, bah" with some light flashing but it didn't sound like an actual fire alarm," Johnston said.

"When the real alarm goes off, you can't fail to hear it, you can barely stay there. You have to get out," Bookel said.

On the way out, the couple screamed "fire" and pounded on their neighbours' doors. No one was injured.

Fire officials believe the fire started on the exterior of the building, crept into the attic and spread from there. Other residents have complained that alarms did not sound.

Johnston and Bookel have made a statement to RCMP and want answers from Shelter Canadian Properties, the company that owns the building.

Company officials declined to comment because the fire is under investigation

With files from the CBC's Tim Adams