An 18-year-old woman is in hospital with injuries that are believed to be life-threatening following a road traffic collision in Poole.
Officers attended the incident, along with the ambulance and fire services, which involved a blue Ford Fiesta Zetec at the Mannings Heath Roundabout on Sunday morning.
A local man in his 20s has been arrested on suspicion of a driving offence and is assisting officers with their enquiries.
Officers are appealing for witnesses or anyone with relevant dashcam footage to come forward.
Road closures weren put in place to allow the emergency services to respond to the incident and for an examination of the scene to take place.
Sergeant Mark Scammell, of the traffic unit said: “We are carrying out an investigation to establish the full circumstances of this collision. I would urge any witnesses to the incident, or the manner of driving prior to the collision, to please contact us.
“I would also like to hear from anyone who may have captured anything on dashcam that might assist our enquiries.
“Finally, I would like to thank members of the public for their patience and understanding while the closures are in place.”
Anyone with information is asked to contact Dorset Police at www.dorset.police.uk/do-it-online/, via email SCIT@dorset.pnn.police.uk or by calling 101, quoting incident number 21:112. Alternatively, to stay 100 per cent anonymous, contact the independent charity Crimestoppers online at Crimestoppers-uk.org or call Freephone 0800 555 111.