An electrical fault is to blame for a fire at the Tuggeranong Indoor Sports Centre on Cowlishaw Street.
ACT Fire & Rescue were alerted to the incident by an Automatic Fire Alarm (AFA) after midnight.
The fire took hold in the wall cavity near courts three and four before spreading to a section of the roof. Firefighters knocked down parts of the wall to access the fire. A large amount of smoke was visible outside the building.
Two pumpers and a commander attended the incident.
Ventilations operations will be conducted before crews leave the scene.
Damage is estimated at $20,000.