North Yorkshire Police say that the man fell from the Spa Bridge, Scarborough at around 7.05pm today (Tuesday).
Paramedics are currently treating the man at the scene and he is due to be air lifted to hospital with serious injuries.
Roads have been closed in and around the scene with local diversions in operation and members of the public are asked to avoid the area until further notice.
The spokesperson added that police are investigating the circumstances surrounding the incident.
Witnesses or anyone with information that could assist the investigation are asked to call North Yorkshire Police on 101, select option 1, and speak to the Force Control Room. Please quote reference NYP-07112017-0410.