The fire was reported from the top two floors of the four-storeyed 109-year-old Gorton Castle, housing the state’s Audit and Accountant General, a fire department official told IANS.
Deputy Commissioner Dinesh Malhotra said fire has been contained, but its cause is yet be ascertained.
Civilian and army fire tenders were pressed into service to contain the blaze.
Sources said that most of records lying in over 60 rooms in the top two floors were completely burnt. Fire-fighters had a tough time reaching the spot as many official vehicles were haphazardly parked within the complex.
Principal Accountant General Satish Loomba told reporters that he came to know about the incident at 4.45 a.m.
Officials said the fire possibly broke out around midnight.
The building, located in the vicinity of the legislative assembly, housed the central secretariat of the British government till 1942.
The office of the Accountant General of India was shifted to the building in 1954.
Built with stone and timber, Gorton Castle was constructed under the supervision of Maj H.F. Chesney and completed in May 1904 at a cost of Rs.14.02 lakh.
In 2004, it was renovated at an expenditure of Rs.1 crore.
A special postal cover on Gorton Castle was released by the Department of Posts to mark its centenary in May 2004.
Shimla, called the “Queen of Hills” by the British was the summer capital of the colonial rupers. It has 91 British-era heritage buildings.