The A1 dual carriageway has been closed in both directions between Dromore and Hillsborough following a serious crash.
The accident was reported shortly after 3.30am on Sunday (October 9).
The road is expected to remain closed until approximately 11am or noon due to an electricity pole damaged in the RTC.
Diversions are in place but motorists who were planning on travelling along this route should leave extra time for their journey.
One person has been taken to hospital for treatment to their injuries.
There are no further details at this time.