Firefighters were called at 13:58 to reports of a blaze involving a timber-framed building currently undergoing construction.
Ten fire engines and two aerial ladder platforms attended the incident in Kingsway, St Mary’s in Southampton.
More than 70 firefighters from stations across the county worked to tackle the fire, which spread to neighbouring properties.
Residents in nearby Hampton Court were evacuated as a precaution.
HFRS worked alongside key partners including Southampton City Council, Hampshire Constabulary and South Central Ambulance Service.
The fire is now out, with six fire crews remaining on the scene damping down.