The A11 was closed in both directions between the Thickthorn Roundabout and Stagg Roundabout after a BMW police car caught fire.
Norfolk Police advised people to avoid the area and take alternative routes.
The car caught fire just before the Wymondham junction travelling southbound and police were called to the scene at 12.20pm.
The road has now reopened to northbound traffic and limited southbound traffic while the site is cleared.
Two Norfolk Fire and Rescue crews attended the scene and used hose jets to extinguish the fire.
No injuries were reported.
It is believed the car was being used for training at the time of the fire.
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