Crews are in attendance at Savoy Court on Town Lane, where smoke has engulfed at least one flat.
Two pumping appliances and an aerial ladder platform appliance have responded to the scene.
No persons are reported to be trapped in the building, however paramedics from the Isle of Wight Ambulance Service are treating a woman in her 80s for the effects of smoke inhalation.
UPDATE @ 15:44 – Firefighters have successfully extinguished the blaze and have used a ventilation fan to clear smoke from the building.
All persons have been accounted for.