A Status Yellow ice warning for the whole country is in place until midday.
Met Éireann is warning of hazardous travelling conditions with icy stretches on roads and footpaths.
It says freezing rain is possible in the southwest, along with freezing fog patches.
Alan O'Reilly from Carlow Weather says temperatures dipped below minus three in some areas overnight.
"It's down to -3.4 degrees at one station, and I can see that man areas are down to -2 or -3 degrees again this morning, so another frosty morning across the country.
"There are some areas in the southwest where the temperatures are a bit higher, but there's also been some showers which have been a mix of sleet and snow."
