Emergency services are at the scene of a serious crash on the A1 between Dromore and Banbridge.
Just one vehicle was involved in the collision.
Police say the road is expected to be closed in both directions for some time.
Drivers are advised that due to a one vehicle road traffic collision this afternoon, the A1 Southbound between Banbridge and Dromore is closed in both directions.— PSNI Road Policing (@PSNITraffic) November 24, 2019
Motorists are advised to seek alternative main routes for their journey.
A PSNI statement said:
Police remain on scene following a serious one-vehicle road traffic collision on the A1 south bound between Banbridge and Dromore.
The A1 is closed in both directions, south bound at the Banbridge Road junction at Dromore, and north bound at the Dromore Road junction, Banbridge.
The road is expected to be closed for some time as police continue with their enquiries and drivers are advised, where possible, to seek an alternative route.
We thank the public for their patience and co-operation.