Firefighters have extinguished a fire in the basement of a 4 level apartment building in O'connor early this morning.

Just after 5am, ACT Fire and Rescue responded to reports of a structure fire on Berrigan Crescent.

Upon arrival firefighter located a fire burning in the basement carpark of the building with thick black smoke coming from the carpark entrance.

ACT Policing also responded to the scene and assisted in the evacuation of residents in the unit complex.

The fire was brought under control at about 6.30am with no reports of injuries.

ACT Policing have launched an investigation into the fire and have forensic police attending the scene today.

Anyone with further information is urged to contact Crime Stoppers on 1800 333 000.