The A27 was closed off from the Havant Road junction in Warblington up to Fishbourne Roundabout for Chichester after a crash last night and it remains shut this morning.
Sussex Police have confirmed that a 25-year-old man from Havant died in the crash at 11.40pm.
A spokesman from the police force said: ‘At 11.40pm on Wednesday, February 10, a black Volkswagen Golf was travelling east towards Chichester on the A27 when it crashed.
‘The driver was sadly pronounced dead at scene. The passenger – a 19-year-old man from Havant – suffered life-threatening injuries and has been taken to hospital for treatment.
‘The road is likely to be closed in both directions between Fishbourne and Emsworth roundabouts for some time whilst the investigation takes place, and motorists are advised to seek alternative routes.’
Police are appealing for witnesses and are interested to hear from anyone with dash cam footage of the collision or the Golf being driven prior to the incident.
Anyone with information is asked to contact police on 101, quoting the reference Operation Westdown.