Met Éireann has warned of significant snowfall tonight and tomorrow with Ulster, Connacht and Leinster expected to be worst-hit.
Strong easterly winds and frost will develop in many places after dark and snow will spread from the south.
"Some significant falls of snow are expected, especially over Connacht, much of Leinster and Ulster, with some drifting in places before dawn," Met Éireann said. Lowest temperatures will be between minus three and plus two degrees Celsius.
Further snow is forecast for tomororw for a time over the northern half of the country in the morning. The cold snap will continue into Friday with further sleet and snow in northern areas.
The Road Safety Authority advised all road users to take special care when using the roads in icy and snowy conditions.
Snow amounts of three to six centimetres are expected generally, but up to 10 cm may fall in the north Midlands and Ulster.
RSA Chief Executive Noel Brett said: "Bad weather such as ice and snow can catch road users off guard. Therefore in such weather conditions it is best to avoid making any unnecessary journeys. If driving in such conditions is unavoidable be prepared. The golden rule is drive with care and expect the unexpected".
Motorists are advised to check weather forecasts, clear windows and mirrors before setting out and to carry a mobile phone. If driving in icy or snowy conditions drivers should drive slowly, allow extra room between your vehicle and the vehicle in front, use the highest gear possible to avoid wheel spin, avoiding harsh braking and acceleration and use dipped headlights.
In the event of a minor skid motorists should release the brake pedal fully and stay off the brake, turn the steering wheel in the same direction as the skid and ease off the accelerator at the same time.
There were hazardous driving conditions across the country this morning after temperatures fell as low as -7 degrees overnight.
There were also been falls of sleet and snow in many parts along the east coast.
Counties Wexford, Wicklow, Kilkenny, Cavan, Monaghan, and Dublin and its hinterland experience dangerous conditions. While there has been less of the heavy, sometimes, freezing fog of yesterday, heavy ice was reported in Co Carlow.
