South Wales Police is investigating a road traffic collision in James Street, Cardiff, at around 3am today involving one vehicle and a male pedestrian.
The 25-year-old pedestrian was taken to the University Hospital of Wales, Cardiff, where he later died.
One man who was arrested at the scene on suspicion of dangerous driving and being unfit to drive through drink or drugs remains in custody.
Enquiries are on-going.
James Street is currently closed and motorists are advised to take alternative routes.
Anyone who witnessed this incident is asked to contact South Wales Police by calling 101.
