Fire crews from stations in Havant and Waterlooville were called out to the blaze on the A3 northbound at Clanfield.
The exit slip road was closed to traffic but has now been cleared.
Police and Highways England are also at the scene to help divert traffic and to manage the road closure.
Photos from the scene show a car had been destroyed by the blaze, with the fire crews leading the investigation into the incident.
Luckily everyone in the car was able to get out safely and no injuries were reported.
There has been a separate vehicle fire this morning on the A3 near Ripley in Surrey.
Two lanes were closed by emergency services while the incident is dealt with.
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