Motorists throughout the country have been urged to take extra care on the roads due to snowfall overnight and this morning.
Ice and snow are causing problems, particularly on minor roads.
Motoring body AA Roadwatch said motorists should use major routes as these were more likely to have been gritted than secondary roads. It said drivers should also reduce speed and use gentle manoeuvres because stopping distances are up to 10 times greater in ice and snow.
Parts of the country affected by heavy snow include Cavan, Monaghan, Drogheda, Wicklow town, Greystones, Navan, Kells, Kilkenny city and Longford town.
Conditions are very icy on the M7 Limerick to Dublin road and gardai were earlier dealing with a collision northbound at Birdhill.
The Dublin road out of Nenagh was closed at Knockalton Cross after a crash.
AA Roadwatch said conditions appeared to be worsening in the midlands, northwest and south. Slane village in Co Meath is impassable and a number of trucks jack-knifed in the area this morning. The approach to the village on the River Boyne is on a notoriously dangerous hill.
Snow has fallen on top of ice around Ennis, County Clare while gardaí are dealing with a number of collisions on the M18 Limerick/Galway road northbound between J15 Cruisheen an the J11 Dromoland.
Snow has also been reported in Carlow, Louth, Westmeath, Offaly, Longford, Wicklow and Wexford.
"Very icy" conditions have been blamed for a number of incidents on the N17 Galway/Sligo road at Achonry, while in Cavan there have been a number of incidents on the Baileborough/Virginia road (R178).
Met Éireann said it would be very cold and extremely windy today with frequent showers, many falling as hail, sleet and snow during the morning and with a risk of blizzard conditions in places. This will turn to rain and hail during the day, with any lying snow melting.
There will be a few bright spells and the showers will tend to become more scattered later, Met Éireann said. Maximum temperatures will be between 6 and 9 degrees.
There will be some further scattered showers tonight, most of them in Ulster, Connacht and west Munster, but more isolated elsewhere, with good clear spells.