A man in his 20s who was cycling on Charminster Road is in a critical condition after being involved in a collision.
The incident, which happened around 11pm Wednesday, resulted in the man being airlifted to Southampton General Hospital.
Officers are appealing for witnesses or anyone with dashcam footage to come forward
The collision involved the cyclist and a stationary red Vauxhall Combo car-derived van on Charminster Road between the junctions of Malvern Road and Claremont Road.
The road was closed to allow emergency services to deal with the incident and treat the injured man.
Police Sergeant Rhys Griffiths, of the traffic unit, said: “We are carrying out enquiries to establish the full circumstances of this collision and I am appealing for any witnesses to please come forward.
“I would urge any motorists who were travelling in the area and have dashcam fitted to their vehicle to please check it for any relevant footage that may assist my investigation.
“Finally, I would like to thank motorists for their patience during the road closure, which was absolutely necessary to enable emergency services to attend the scene in a safe manner and provide medical treatment.”
Anyone with information is asked to contact Dorset Police at www.dorset.police.uk, via email at scit@dorset.pnn.police.uk or by calling 101, quoting occurrence number 55210100419.