2 pumping appliances and an aerial ladder platform from Newport are in attendance at the scene on the junction of West Street, Drill Hall Road and The Mall.
Emergency services were alerted to the incident just a short time ago at 16:00.
The roof of the residential building is said to be alight.
No one is thought to be trapped or injured, although some pet birds have been rescued from the block.
Firefighters are continuing to dowse the flames and are bringing the incident swiftly under control.
The Incident Command Unit is on scene alongside several Police units and the Isle of Wight Council Emergency Planning Officer.
UPDATE @ 17:00 – A total of 6 pumping appliances – 2 from Newport, 2 from Ryde, 1 from East Cowes and 1 from Cowes – and an aerial ladder platform (ALP) from Newport are on scene, although the fire has been brought under control.
2 firefighters are removing tiles from the damaged roof and are damping down using the ALP.
Cordons are in place.
UPDATE @ 17:30 – Station Officer James Lucy has confirmed that fire crews are tackling a fire on the 2nd floor, which had broken through the roof of the building by the time the first crews arrived on scene.
The blaze has been largely extinguished however firefighters are continuing to check for any remaining hot spots to ensure the fire is entirely out.
Station Officer Lucy has said the cause of the fire is currently unknown but that an initial investigation is expected to get underway in around an hour or so.
The Isle of Wight Ambulance Service is standing by due to the size of the incident.
UPDATE @ 18:00 – The incident has now been scaled back to 5 pumps plus the ALP and is expected to be scaled back further shortly.
Pyle Street has been closed and the flow of traffic reversed. West Street, Drill Hall Road and The Mall also remain closed alongside the top end of the High Street.
With the situation under control, appliances are making up in preparation to return to station. 3 remain on scene alongside the aerial appliance.
The British Red Cross Fire and Emergency Support Unit is providing support to those affected by the fire and firefighters are collecting personal possessions, where possible.
The cause of the blaze is yet to be confirmed, but is thought to have started in the loft space.
Residents are to be rehoused overnight, possibly in the nearby Travelodge.
UPDATE @ 21:15 – The Isle of Wight Fire and Rescue Service have now left the scene, bringing the incident to a close.
Investigators are set to return at 09:00 tomorrow morning to conduct a thorough investigation alongside Police, who remain on scene tonight.
The main through road between Newport and Carisbrooke has reopened in both directions, however West Street remains closed due to concerns over the structure of the damaged building. Fencing has been put in place.
Locals have praised the efforts of local contractor Blake Ashton and his work force, who spotted the fire and raised the alarm before helping residents evacuate.