Propane tanks had to be quickly removed by firefighters, who feared the situation could quickly get "very dangerous".
As many as 40 firefighters were on the scene at Williams Garage in Otterbourne.
The blaze broke out around 3.30am and more than three hours for Hampshire Fire and Rescue to get under control.
The main building has been 80 per cent destroyed by the fire, with the roof collapsing in as well. A unit at the rear has also been wrecked, as have around 20 vehicles.
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Fire crews were able to stop the flames spreading to the adjacent former filling station and garages at the rear of the property, which are attached to homes.
Main Road was closed in both directions, but reopened at 8am.
The building measured 32 metres by 15 metres and was used as a garage, workshops and offices.
Ten breathing apparatus, seven jets, one compressed air jet were used to extinguish the fire.
Appliances from Eastleigh, Winchester, St Mary's and Redbridge are attending the incident.
No-one was injured in the fire, or needed to be evacuated from nearby properties.
Firefighters are remaining on the scene damping down, while police officers are now beginning an investigation into the cause of the fire, which is believed to have started in one corner of the main building.
The village shop, which is attached to the building, has not been damaged but is currently closed. ©UKNIP