A red alert weather warning has been issued after the "Beast from the East" polar system dumped several inches of snow on parts of Ireland.
Met Eireann upgraded its advice to the highest level and cautioned that up to 10in (25cm) of snow could fall by Thursday.
Up to 4in (10cm) has already been recorded in counties in the east.
The red alert covers Dublin, Kildare, Louth, Wicklow and Meath and is active until midday on Thursday.
The public are being advised to expect widespread disruption.
Dublin Airport has reported a number of flight cancellations.
Luas services are operating in the capital but on a limited basis.
Dublin Bus has kept services running on main roads.
And Irish Rail said all its services are running, including commuter trains but with delays on some lines and that it will try to give as much notice as possible of disruption.
School buses are automatically stopped during a status red weather warning, effectively closing schools in the east.
Several inches (centimetres) of snow was reported in Dublin, Kildare, Wicklow and further north, with lower levels reported in the Midlands.
The National Emergency Co-ordination Group met in Dublin on Tuesday and warned the public to prepare for an exceptional weather event.
Further planning and response meetings will take place on Wednesday.
The snowfall is expected to be compounded by the arrival of Storm Emma as it moves over Ireland on Thursday afternoon, causing further heavy snow across large parts of Ireland, with the cold weather set to last until the weekend at least.
Met Eireann has also issued a mid-level orange alert for snow-ice in Cork, Waterford and Wexford until Thursday lunchtime.