Dorset Police received a report at 5.02am on Sunday 21 November 2021 of a single vehicle road traffic collision involving a blue Ford Fiesta Zetec at the Mannings Heath Roundabout.
Officers attended, along with the ambulance and fire services. An 18-year-old woman was taken to hospital for treatment to injuries that are believed to be life-threatening. Her family has been informed.
Road closures were put in place to allow the emergency services to respond to the incident and for an examination of the scene to take place. They were lifted at around 2pm.
A local man in his 20s was arrested on suspicion of driving offences and is assisting officers with their enquiries.
Following further enquiries, a man from Surrey aged in his 20s was also arrested on suspicion of driving offences and is also assisting with enquiries.
Officers are continuing to appeal for any witnesses or anyone with relevant dashcam to come forward.
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.