Emergency services were called to the landmark building in Dudley Road at around 17:30, with crews from Ventnor, Shanklin and Sandown responding.
2 appliances are on scene alongside an aerial ladder platform from Ryde. The Incident Command Unit from Newport has also been mobilised alongside a duty officer.
Firefighters wearing breathing apparatus have entered the building.
The one-way road has been closed to traffic while the incident is being dealt with. A cordon has been erected.
Salisbury Gardens is the location of Ventnor Town Council and Ventnor Police Station. It also plays host to a number of offices.
UPDATE @ 19:00 – Firefighters are investigating the cause of the alert, which is said to have been caused by smoke setting off automatic fire alarms.
The cause of the smoke is believed to have been caused by a faulty light socket.
The Arial Ladder Platform from Ryde has now left the scene.