Lincolnshire Police are treating a fire at a former sweet factory in Skegness as arson.
The fire was started at the old Fravigar sweet factory on Heather Road between 4pm and 5pm on Saturday, July 22.
The site is not in use and boarded up but officers believe someone gained access and started the fire deliberately.
Severe fire damage was caused to a quantity of polystyrene panels within the derelict warehouse.
Smoke damage was caused to the remainder of the building.
Anyone who was in the are at the time and witnessed suspicious activity should call Sergeant Andrew Price on 101, quoting incident number 321 of July 22.
Alternatively, contact the independent charity Crimestoppers anonymously on 0800 555 111.