A woman in her thirties is in a serious condition in hospital after two vehicles collided on the A21 Bangor/Ards carriageway on Saturday night.
The collision occurred on the Ards-bound carriageway at the junction with the Green Road at around 11.20pm and involved a red Audi and a blue Renault.
Three men and a woman were taken to hospital. While the woman is in a serious condition the men suffered non-life threatening injuries.
Two men aged 22 have been arrested in relation to the collision and one remains in custody.
The road was closed for a time after the crash but has since reopened.
Inspector Jonathan Francey has appealed to anyone who witnessed the collision or who saw either of the vehicles involved travelling in the area before the collision to contact police in Newtownards on 101 quoting reference number 1481 18/02/17.