Crews from Sleaford, Metheringham, Woodhall Spa and Lincoln attended the call at 2.17pm and are said to be still on the scene.
Nearby residents were advised to keep their doors and windows closed.
A spokesman confirmed the incident involved three vehicles in a single storey garage.
Police were also called and were said to be assisting at the scene, the building and two of the cars were completely destroyed in the fire. No-one is said to have been hurt.
A police spokesman added that there was nothing to indicate any suspicious circumstances at this stage.