An apartment fire in Fort McMurray this week started on the second-floor balcony on the north wing, say investigators.

The Parson's Landing complex fire, which started at 11:30 Sunday, is not considered suspicious, say firefighters.

What started the fire is not yet known.

The north wing of the 160-unit building was destroyed in the fire.

Nobody was hurt, but many residents said they had no warning until neighbours or firefighters pounded on their door, yelling to get out.

Investigators also said that fire alarms in the building had an insufficient power supply, causing many not to sound.

The sprinkler system did work, however, which helped stop the fire from spreading further, they said.

They also said the explosions heard by residents during the fire was a propane tank on a balcony.