Police are appealing for witnesses following a serious collision in Clifton Road, Littlehampton, on Tuesday (September 6).
A grey and red Lexmoto 125cc motorcycle is reported to have collided with a wall at around 1pm.
Its rider, a 36-year-old man, was taken to hospital with serious injuries. His next of kin have been informed.
Three men from Littlehampton – two aged 23, one aged 19 – have been arrested on suspicion of causing serious injury by dangerous driving and released under investigation while enquiries continue.
Anybody who witnessed the incident, the circumstances around it or has any relevant footage is asked to contact police.
Investigating officers are also appealing for witnesses or footage in relation to any cars being driven erratically around the time of the collision.
Information can be reported online via the Sussex Police website, 101 or through email@example.com, quoting Operation Glenmoy.