Two male patients are in Belfast’s Royal Victoria Hospital – one in a critical state, the other stable – following a two-vehicle crash between Carryduff and Ballynahinch.
Police say two vehicles were involved in the accident, and announced that they had closed the main road between the two Co Down settlements at around 9pm on Wednesday.
Diversions are in place via Carr Road and Drumalig Road.
The Northern Ireland Ambulance Service had told the Belfast health trust that six people had been involved in the accident.
Some were treated at the scene.