All of the Irish Republic has been put under the highest weather warning - red alert - as the worst snow in 35 years hits.
The decision was taken by forecasters in Met Eireann at 11pm on Wednesday night over the threat of snow and ice.
It runs until Friday at 3pm.
"Blizzard conditions will develop from the south on Thursday afternoon and evening as heavy snow and strong easterly winds bring snow drifts northwards over the country," Met Eireann said.
"Eastern and southerly counties will be worst affected."
Up to 25cms of snow is expected in some areas, with predictions that accumulations could hit 40cms.
People across a huge swathe of the country are being advised to stay indoors.
All non-emergency services are to shut down, including schools and hospital outpatients and admissions services, amid potentially life-threatening Arctic weather and blizzards.
The severe winter conditions are a result of the combination of the Beast from the East polar air system and Storm Emma moving in from the south.
It is expected to hit Ireland harder than anywhere else, and it is predicted to be the worst snow storms since 1982.
The public have been urged not to travel in Leinster and Munster, the south and east of the country.
Blizzards are expected to strike the south coast from 4pm on Thursday afternoon as the polar conditions mix with Storm Emma's gales, up to 100km/h.
Drivers have been warned there will be zero visibility.
Appeals are also being made for people to check in on elderly neighbours and to report sightings of rough sleepers.
Taoiseach Leo Varadkar appealed for people to heed the advice.
Sean Hogan, senior official in the National Emergency Co-ordination Group (NECG) which oversees planning for major weather events, put the forecast in context.
"We have not experienced blizzard conditions since 1982 and reports from that time indicate the serious and life-threatening conditions which may be posed by the combination of heavy snow and strong winds," he said.
"The NECG is advising that people should not venture out of doors while the red level warning is in place in your area."
Schools, airports, rail, bus and tram travel, creches and childcare facilities are all being impacted.
All public services, except emergency response and inpatient services in hospitals, are also being scaled back.
With the red alert extended, all schools will close.
Met Eireann also said that the snow will continue until the weekend, including some wintry showers on Saturday.
Transport Infrastructure Ireland, which oversees main roads around the country, said it is aiming to keep all major national routes open.