Police said the man was driving a silver Landrover Freelander when it left the Sutton Bridge carriageway near the Market Lane junction, plunging into a ditch after a collision with a fully laden green Volvo articulated lorry at 6.30am.
Police closed the road for five hours whilst the man, in his 70s, was treated for head injuries that a police spokesman described as 'life altering'.
PC Mark Howes, Swaffham Road Policing, would like to hear from anyone who witnessed the incident or the manner of driving of either vehicle prior to it. Ambulance service spokesman Gary Sanderson said: 'A man who we believe to be in his 70s has been taken to Queen Elizabeth Hospital, in King's Lynn, with a head injury.'
A Norfolk Fire spokesman said: 'Two appliances from Kings Lynn and Terrington and the heavy rescue pump from Kings Lynn attended a road traffic collision.
'The crews extricated a casualty using hydraulic rescue equipment, administered casualty care, assisted the ambulance service and made the vehicles safe.'
Anyone who saw the crash is asked to call PC Howes on 0845 456 4567.
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