Motorists were warned to avoid driving near the Wicklow mountains tonight due to dangerous road conditions.
Gardaí appealed for people not to travel around the Sally Gap, Glenmalure and Aughavanna as emergency services have no access to the areas.
AA Roadwatch said conditions are also icy on secondary routes in Ulster, Connaught and Leinster.
Extreme care is advised in Kerry and Galway where snow is falling.
Assistant Garda Commissioner Kevin Ludlow earlier advised all road users to be wary of the dangers when driving.
“It is important to realise the conditions differ significantly right across the country and indeed the overnight thaw has probably left some of the roads in a more aggravated condition,” he said.
“It is very important that motorists and indeed pedestrians recognise that there are several dangers out there, particularly in shaded untreated areas.”
Met Eireann forecast the cold snap will continue over the coming days, with falls of rain and sleet everywhere overnight.
The New Year will bring frost, ice and freezing fog, with temperatures expected to fall to -5C on Thursday night.
In the Mid West region, drivers were also urged to drive with extreme caution as heavy snowfall is expected to lead to extremely difficult conditions.
Clare County Council said seven road gritting crews have been covering 580kms of road network during the Christmas period.
Meanwhile the Mayor of Clare, Councillor Tony Mulcahy, called on residents to ensure elderly neighbours are kept warm and have enough food during the cold weather.
“Older people, particularly those living in isolated areas, are more vulnerable during colder spells of weather,” he said.
“Those who are elderly and living alone should be checked on by neighbours, morning and evening.
“Practical help can be given by bringing in solid fuel, ensuring the water supply is sufficient and checking that there is sufficient food in the house, including non-perishable foods.”