The fire at Don River heritage rail centre in Tasmania was accidentally lit, with the likely cause being restoration work on a carriage, authorities say.
Tasmania Fire Service and Tasmania Police completed the investigation this afternoon.
Volunteers say they are "absolutely devastated" after parts of the Don River heritage rail centre were destroyed by fire.
Fire crews from Devonport, Burnie and Latrobe were called to the blaze in the early hours of Tuesday morning and found three warehouses, containing carriages and wood working equipment, fully alight.
About 30 firefighters helped bring the blaze under control but the carpenter's centre was destroyed and water damage caused to the Don River Railway function centre.
Mark Brownrigg, district officer with the Tasmania Fire Service, said it was not yet clear what had happened to the carriages inside the workshop.
"Three main sheds have been involved in fire, two housed carriages that had been restored and one was the function centre," he said.
"Due to the complexity of what's happened it's unclear how much damage has been caused to the north side of the building."
The vintage railway has carriages and steam engines dating back to the late 1800s and is owned and operated by volunteers.
Don River Railway president Lynn Laycock said she was "devastated".
"It looks like we've lost a carriage shed and a couple of carriages that were being renovated and a lot of machinery.
"I'm devastated, for all the thousands of hours of work that's gone into the restoration."
Ms Laycock said she understood the shop, offices and museum were untouched but the function centre would be out of action for some time.
"We've got a lot to work through. I don't think we've ever been closer to getting the main line running and getting the train onto the main line but it will happen believe me, because everybody will dig in even harder than they've done in the past.
"Nobody wants to wake up to a call like that in the early hours of the morning."
