A South Yorkshire Fire and Rescue spokesman said the fire was initially believed to have started at HMP Lindholme, but has now confirmed that the blaze is located at a building next to the prison.
They added: "Six fire engines are currently at a building fire on Bawtry Road in Hatfield Woodhouse, Doncaster.
"A large furniture storage building next to HMP Prison Lindholme, has been destroyed by fire.
"The building is outside the Prisons boundary wall.
"Fire crews from Thorne, Adwick, Doncaster, Rotherham, Barnsley and Epworth (Humberside Fire & Rescue) were called to the incident at 12:15pm on Thursday."
Firefighters have been tackling the blaze with hose reels and as at 2pm the fire is now under control and crews are damping down.
There are no reports of any casualties.
An investigation into the cause of the fire will take place once the fire is completely out.
An eye-witness said of the fire: "I saw massive plumes of smoke coming from the fire from as far away as Bawtry."
The cause of the fire is not yet known.
This is a breaking news story, and will be updated as more details come in.