The main Dublin to Belfast road remains closed as Army Technical officers continue to examine a suspect vehicle just outside Newry.
The road is likely to remained closed for several hours.
The security alert began at 11pm last night following two bomb warnings to a hospital and a charity organisation.
The PSNI closed the southbound carriageway from the Sheepbridge interchange, north of Newry city.
Diversions are in place on the M1 from Junction 18 northbound. The A1 remains closed from the M1 up to the Sheepbridge Interchange, north of Newry.
Elsewhere, the PSNI is responding to two security alerts around Strabane in Co Tyrone.
One is near the town's police station and another on the Strabane to Omagh road.
Earlier, British Army bomb experts carried out controlled explosions on two suspect devices found in Lurgan in Co Armagh. Both were later declared hoaxes.
