Travel service Romanse report the incident on the A3023/Havant Road is partially blocked in both directions near Victoria Road due to the blaze amid sweltering temperatures.
The incident has caused delays in both directions of about 20 minutes.
It was reported at 2.51pm.
Fire crews are thought to be on the scene.
No details have been released about those in the car.
It is not known what caused the fire at this stage.