Updated on Feb 5 at 11.34am: One fire engine remains at the service garage in the east of Lincoln to cool acetylene cylinders and extinguish any hot spots.
There was severe damage to five vehicles and tools at the premises.
An area 75 meters around the premises has been evacuated and some eight crews attended the incident that was first reported at 3.42pm on Monday.
Two fire engines remained overnight to monitor the fire.
The incident is at the Riccardo Emiliani unit on Wrightsway, off Outer Circle Drive. The fire started on the ground floor.
It is still unclear what started the fire, which was emitting a black smoke.
No one was hurt.
Fire and Rescue used four breathing apparatus, one hose reel and two main jets.
Photos from the scene from Lee Shear, Andy Hibberd and Lincoln Jaguar