Crews on 10 fire engines are at Luckington Manor this afternoon fighting what police describe as a major blaze.
Police have closed all roads around the manor, which is owned by the family of a sheikh who died last year.
The fire service says the first emergency call was received at 1.16pm today. They say there are no reports of any injuries.
A fire brigade spokesman says the fire has affected the first floor and the roof. Because there are concerns about the structural integrity of the building, all firefighters have been withdrawn from the interior of the building.
Villager Richard Marshall told the Gazette at 2.45pm that the roof of the building had just collapsed.
He said: "I could see flames coming from bedroom windows. There is a colossal amount of smoke."
Villagers have not been told to stay indoors and many are gathering as close to the manor as possible to watch the drama unfold.
A spokesman for the fire service says crews from Malmesbury, Chippenham, Tetbury, Corsham, Westleigh in Swindon, Cricklade, Melksham, Calne, Dursley and Bradford on Avon are at the scene.
An aerial appliance and incident support vehicle have also been sent.