The collision involving a single motorcycle occurred on Layerthorpe outside National Tyres and Autocare at around 11.30am today (Tuesday 29 November 2011).
The motorcyclist, a local man believed to be in his 30s, suffered serious head injuries in the incident and has been taken to York District Hospital for treatment.
Layerthorpe is currently closed in both directions between James Street and Foss Islands Road as police investigate the circumstances surrounding the collision.
Traffic is currently being diverted along James Street and Foss Islands Road.
Officers are appealing for anyone who witnessed the collision to contact North Yorkshire Police on 0845 60 60 24 7 – select option 1 –quoting reference number NYP-29112011-0132.