ACT Fire & Rescue was called to the incident on McIntyre Street just before 8pm.
The fire was quickly extinguished. Damage was extensive.
Crews found the apartment unoccupied after a primary search. Surrounding areas have been evacuated as a precaution. The cause of the fire is still being investigated.
Three pumpers, the Breathing Apparatus Van, Bronto aerial unit and two commanders are expected to remain on scene for another thirty minutes.