A passer-by called the Tasmania Fire Service at 11am after seeing thick black smoke coming from a garage attached to the showroom.

Longford Brigade chief Mike Armstrong said crews from Longford, Perth and Launceston arrived 10 minutes later and gained entry to the garage through a small door.

``We found a vehicle on fire within the shed, promptly put the vehicle out and ventilated the space,'' Mr Armstrong said. ``At this stage it's looking like an electrical fault with the Honda.''

A Volvo parked in front of the Honda had damage to its rear end while an AMG E55 Mercedes parked inside the garage was removed undamaged by the owner.

The cars in the showroom were also undamaged but smoke affected the rest of the building and showroom.

Mr Armstrong said it was very lucky that a passer-by saw the smoke and called triple-0.

``You just don't know with these incidents, another five minutes later it could have been a completely different scenario,'' he said.

``There's quite a good variety and an expensive variety of vehicles here, so to limit it to that one vehicle and slight damage to another was a really good job by the fireys to do that.''

The owner declined to be interviewed.