Police were called at 9.20am to reports of a collision between a white lorry and two pedestrians on the A1065.
One of the pedestrians, a teenage girl, was pronounced dead at the scene.
The other pedestrian, a woman in her 50s, was taken by air ambulance to Addenbrooke's Hospital where she remains in a critical but stable condition.
An East of England Ambulance spokesman said: 'We received a call today at 9.20am to reports of a serious RTC involving two pedestrians on the A1605 at West Lexham.
'We sent two rapid response vehicles, two ambulance crews, an ambulance officer and two helicopters from the East Anglian Air Ambulance.'
The crash scene is on a hill around half a mile north of All Saints Church.
The A1065 was closed between Castle Acre and the B1145 whilst emergency services deal with the incident. It has now re-opened.
Anyone who saw the collision or the moments leading up to the incident should contact PC Keith Wiseman on 101.
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