Latest: Met Eireann says the worst is over but low temperatures expected all week
Met Eireann says the worst is over weather wise but it is going to stay cold all week.
Temperatures dropped as low as minus 8 just before dawn, and should reach no more than 4 degrees later.
Snow, ice and slush on the roads have caused travel disruption, while schools in parts of the West, North West and Midlands are closed.
Forecaster John Eagleton says conditions are about to improve a little.
He said: "The worst is over in the sense that temperatures will be lowest today and last night, for the rest of the week they are going to stay low but they won't be quite as low as they were.
"The coming night will be frosty with temperatures down to minus 3 but it will clear more quickly Tuesday morning."
An Post has said it will make deliveries if it is safe to do so.
The company says its closely monitoring local road conditions in affected areas and will continue to assess the situation throughout the day.
Cold weather is causing school closures, flight cancellations and treacherous road conditions.
Temperatures plummeted to minus 8 in places - while snow, ice and slush is making travel dangerous.
Irish Rail says all trains are running but some services are facing delays - while Dublin airport says five departures to Heathrow Airport are cancelled because of poor weather in London.
The AA's Gemma Ryan has warned road users.
She said: "According to reports, the worst affected counties appear to be Galway, Roscommon, Sligo, Donegal and Cavan with widespread frost across the country.
"When driving in such conditions use your dipped headlights and remember stopping distances are up to ten times longer in ice and snow, so leave plenty of space between your car and the car infront and allow yourself extra time to reach your destination."
There is a low temperature warning in place across the country and road users are being urged to take extreme care.
It started yesterday morning and will continue until 10am today.
Overnight lows of minus 8 degrees were recorded in some parts with snow heaviest in east Connacht, Leinster and Ulster.
Met Eireann meteorologist Liz Gavin says it should improve slightly later today.
She said: "We can still expect to see some icy conditions at first this morning, some treacherous conditions on any untreated surfaces, cold still today with highest temperatures of 3-6 degrees, temperatures slightly improving on recent days but still quite cold."
