A Status Orange warning for snow and ice has been issued by Met Éireann for seven counties.
The warning, for counties Cavan, Monaghan, Donegal, Longford, Leitrim, Mayo and Sligo, came into effect at 4pm.
It is to remain in place until 6pm tomorrow, with accumulations of 4 to 8cm expected. These may be greater on higher ground.
Temperatures are expected to plunge below zero overnight for most of the country.
The public are also warned to be aware of icy roads and footpaths.
A Status Yellow snow and ice warning is also in place for the remainder of the country, where accumulations of up to 3cm are expected.
The Met Office has also issued a Yellow warning for snow and ice across Northern Ireland. That warning will be in place until midnight.