Both lanes are blocked near the church at East Winch after collision between a car and a lorry.
Police said diversions were now in progress and the road was likely to remain closed for several hours.
The crash happened just before 12.30pm, blocking both lanes of the A47 near the church.
An East of England Ambulance spokesman said an ambulance crew, ambulance officer, and the East Anglian Air Ambulance were sent to a report of a man who was trapped.
'They treated a man, believed to be in his 60s, who has a suspected broken leg and chest pain,' he said.
'They are still on scene, but will be taken to Queen Elizabeth Hospital soon by land ambulance.'
A police spokesman said: 'We received a call at 12.22 hours from a member of the public reporting a two vehicle collision involving a lorry and a car.
'Police arrived on scene at 12.32 hours, the fire and rescue service and the ambulance service are also in attendance and remain so at this time. Specialist Roads Policing officers are on scene conducting a detailed investigation and currently an elderly male is receiving medical treatment for injuries, the extent of which are at this stage unknown.'
The road remains closed between Constitution Hill and the A47/A1122 Roundabout at Swaffham. First Buses say services are unable to reach Middleton or East Winch.
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