A fire has extensively damaged a McKellar house.

The ACT ESA said fire crews were called to the Dumas Street house at about 8.30pm on Tuesday to find the garage completely on fire.

The fire quickly spread to the rest of the two-storey home.

It took six fire brigade units about an hour to extinguish the blaze.

The cause of the fire is not known.

Firefighters were alerted to the fire by multiple triple-zero calls including from an occupant inside the property who was safely evacuated.