Updated at 5.20pm: Firefighters are tackling a huge blaze in North Hykeham at the Specialist Heat Exchangers building on Freeman Road.
Police are advising people in the area to keep their windows and doors closed due to the potentially toxic smoke.
Lincolnshire Police are asking people to avoid the area while firefighters are dealing with the incident. All adjoining roads have been closed for the next four to five hours.
The fire was reported at 3.02pm. Nine fire crews are in attendance as it stands, one from Lincoln South, Metheringham, Brant Broughton, Gainsborough and North Hykeham; and two from Lincoln North and Newark.
No one has been injured and police said all SHE staff have been accounted for.
The fire spread very quickly as thick smoke swept across the surrounding area.
Lincolnshire Police drones showed the flames from above.