Fire Rescue Victoria (FRV) crews responded to reports of a flat on fire in Thornbury about 4:30am after multiple calls to triple zero.
Crews arrived on scene within three minutes to find smoke and flames issuing from a flat on the second storey of a brick unit.
Firefighters donned breathing apparatus and began an internal attack on the fire and protected adjoining flats.
No occupants were found in any of the fire-affected flats.
The fire was deemed under control by 5:30am.
The cause of the fire has been deemed suspicious.
Police are investigating.
