Update - House fire in Gordon

The fire has been extinguished.

Initial investigations indicate the fire started in an unattended bedroom and quickly spread to the roof space.

The occupants were alerted to the fire by a smoke alarm sounding.

The building has sustained serious damage to the roof and bedroom.

The initial damage bill has been estimated at $500,000.

"The occupants were very lucky to escape the fire safely and raise the alarm," ACT Fire & Rescue commander Leigh Curtis said.

"This is another example of how working smoke alarms save lives," he said.