Heavy snow and ice have disrupted schools and businesses in parts of Connacht and Ulster where sub-zero temperatures have also resulted in treacherous road conditions.
Up to 13cm of snow has fallen in parts of the north as temperatures dipped to minus three Celsius.
More than 100 secondary, primary and kindergarten schools in the West and Ulster are closed today.
Many local community meetings planned in the west tonight have also been cancelled because of dangerous driving conditions.
There have been reports of many road collisions, none serious. A school bus was involved in a minor accident at Clonberne near Tuam in Co Galway but nobody was injured.
In Northern Ireland, all main roads were reported to be passable this morning with extreme caution, but only one lane on the M1 motorway was open.
Motorists on the Glenshane Pass in Co Derry, traditionally one of the worst affected routes, were advised to negotiate the road with care.
Traffic has returned to normal on the main A5 road between Derry and Strabane after a stranded lorry that earlier caused long delays was removed.
Cold snap set to last until Sunday
Met Éireann has issued a severe weather alert, saying the cold snap will continue until Sunday. Scattered hail and snow showers are set to be most frequent over the north and west.
Moderate accumulations of 3-5cm of snow can be expected in places, with higher accumulations likely over high ground.
Widespread severe frost will occur at night and road conditions will be dangerous.
