Firefighters have extinguished a unit fire in Kambah overnight.

Just before 1am, ACT Fire and Rescue responded to reports of a structure fire on Kett Street.

Firefighters arrived to find a second level unit well alight with smoke spreading through adjoining units.

The fire was contained after an hour, but the home sustained significant damage.

An ACT Policing spokesperson said no people were home at the time of the fire, and the cause of the fire has been deemed suspicious.

Anyone with information about this incident is asked to contact Crime Stoppers on 1800 333 000 or via www.crimestoppers.com.au quoting 7618240.