West Sussex Fire said crews were sent to the incident in Old Brighton Road North, Pease Pottage, at 1.33pm on Saturday (July 10).
Fire engines from Crawley Horsham and Turners Hill were called to the scene alongside an off-road vehicle and the incident command unit from Haywards Heath.
The fire has been brought under control, the spokesman said, with crews remaining on scene to turn over and dampen down.
There are no reports of injuries.
A spokesperson for West Sussex Fire and Rescue Service said: “We were called at 1.33pm to reports of a fire involving a domestic garage on Brighton Road North in Pease Pottage.
“Joint Fire Control mobilised fire engines from Crawley, Horsham and Turners Hill to the scene along with an off-road vehicle and the Incident Command Unit from Haywards Heath.
“Firefighters wearing breathing apparatus brought the fire under control using one hose reel and a fog nail.
“Residents living nearby were urged to keep their doors and windows closed while the fire was extinguished.
“Crews remain on scene turning over and damping down, and are using a thermal imaging camera to ensure there are no further hotspots.”
Traffic reports say Old Brighton Road North remains closed.