The car crash happened on the B2177 in Southwick at 11.17pm.
The 19-year-old victim from Portsmouth was a passenger in a silver Nissan Almera when the car left the road near the junction of Pitymoor Lane.
Another passenger, an 18-year-old from Emsworth, suffered life-threatening injuries and is currently in Southampton General Hospital.
Two people have been arrested following the crash.
Police have announced that a 21-year-old man from Portsmouth has been arrested on suspicion of causing death by dangerous driving and is in custody being questioned by officers.
A 24-year-old man, also from Portsmouth, remains in custody.
Flowers have been laid at the scene and one message said: “Always in our thoughts. God Bless.”
Another said: “Always in our thoughts. Taken too young.”
The names of those involved have not yet been released by police.
A police statement said they were in the process of informing next-of-kin.
Police are appealing for information. Anyone who saw what happened should contact the Serious Collision Investigation Unit at Eastleigh on 101, quoting Operation Chapman.
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