The fire was well alight when multiple crews from St Mary’s, Redbridge, Hightown, Eastleigh, and Hythe arrived at the scene.
The outbuilding contained roughly 3,000 reels of highly flammable cine nitrate film and movie equipment, and was used as a private cinema theatre.
Working throughout the night, the fire was brought under control but carried on well into the following day.
Crews worked with Southampton City Council during the incident, which saw the closure of Hill Lane for a period of time.
By 08:00 on Tuesday 3 December, the incident was scaled down to three appliances at the scene.
Twelve breathing apparatus’, one main jet, one hose reel jet, compressed air foam solution, and one ultra high pressure lance were used to tackle the fire.
The building and its contents were 100% destroyed by fire, with the tiled roof also collapsing.
The cause of the fire was identified as accidental from a nearby bonfire.
Residents of the surrounding area were urged to keep windows and doors closed due to a large smoke plume caused by the fire.
Group Manager Mick Thompson said, "the fire involved a private collection of cine film of which the majority has been lost.
“With our help the fire has burned itself out, which is why crews have been on the scene for an extended period of time.
“From the very start this was a real team effort, and I cannot thank our firefighters enough for all the tireless hours they’ve put into resolving this incident."
The stop message eventually came in at 08:14 on Wednesday 4 December, where the incident was handed over to the owner.