There have been reports of icy conditions on routes through the Craigavon, Banbridge and Larne areas amid a cold start to Friday morning.
A lorry overturned on the Tandragee Road, near Jerrettspass in Newry.
Part of the road was closed for several hours but it has now reopened.
A statement from the Roads Service said: "Icy conditions forecast in the south of the province in Counties Down and Armagh. Salting is being undertaken.
"Drivers should take care especially on untreated roads."
Motorists in the north and west have also been warned of cold temperatures and a risk of icy patches forming on the roads.