Daredevils have been warned to stay indoors during what will be an unprecedented "white-out" in parts of the country tomorrow.
Accumulations of snow are now expected to reach 40cm by Friday in what is predicted to be the most severe weather event in recent years.
Met Éireann have extended their Status Red weather warning, in place until 3pm on Friday, to all counties. The warning was issued at 11pm on Wednesday night and came into immediate effect. The east and south will be worst affected.
Storm-force winds are also expected.
Taoiseach Leo Varadkar has now called on people to "take heed of the warnings".
He warned that it is not a time for "daredevils".
"We're in red alert, everybody should stay indoors," he said.
In an 'address to the nation', Mr Varadkar said there is a real risk to life over the next 48 hours.
"Bear in a mind that in a blizzard scenario, people might not even be able to see the hand in front of their face," he said.
Mr Varadkar asked people to heed of the warnings and "not to risk life or risk limb by going out in the snow or engaging in daredevil activities".
He said children should be allowed enjoy playing in the snow but by tomorrow afternoon Leinster and Munster need to enter shutdown between 4pm tomorrow and midday on Friday.
The Taoiseach described the expected blizzard as a "total whiteout".
"I'm confident we are as prepared as we can be," he said.
Mr Varadkar confirmed that emergency services will be "constrained" at the height of the storm.
He said ambulance and fire crews should only be called out to "genuine emergencies".
"They will be constrained in their operations as well because of the hazard road conditions and winds and snow," he said.
Transport Minister Shane Ross said buses and trains will face "controlled disruption".
He said commuters needed to remember the drivers and other staff needed to get home and stay safe as well.
Mr Ross said the "drama of the situation" was "almost unprecedented", adding that 25cm of snow will accumulate tomorrow before rising to 40cm on Friday.
"It represents a real challenge to people. People must stay at home," he said.
"We'll have public transport back as soon as is safe."
A red weather warning has only been issued on six occasions since the system was introduced in 2013 – and only for rainstorms, never for snow.
"It is very exceptional. It’s not normal," Met Éireann forecaster Evelyn Cusack said.
Storm Emma is due to connect with the ‘Beast from the East’ from late afternoon tomorrow, meaning conditions worsen. This will first hit in Cork, Waterford and Wexford, before spreading across most parts of the country.
"What’s happening is the cold polar easterly air will produce some showers (of snow)," Ms Cusack said.
"As Emma moves in, it’s going to clash with the cold polar air and that’s producing the continuous snow we’re forecasting for Thursday and Friday accompanied by strong to gale force easterly winds. We’re taking about maybe 100 or 110kmh (winds), affecting chiefly easterly and southern areas, and there’s high tides as well."
She said the snow was expected to be “"pretty significant", and sub-zero temperatures were likely to remain in place over the weekend.
While the maximum daytime temperatures would be 1C, with wind chill it would "feel like -5C", she added.
There are currently five weather warnings listed on Met Éireann's official forecast.
A status red snow-ice warning is in place for Dublin, Kildare, Louth, Wexford, Wicklow, Meath, Cork and Waterford. It is in place from Wednesday 8pm until Thursday noon.
It reads; "Further disruptive heavy snow showers are expected overnight with significant accumulations."
A status red snow-ice warning for Munster and Leinster is in place from Thursday 4pm until Friday noon.
It reads; "Blizzard-like conditions will develop in heavy snow and strong easterly winds on Thursday evening and will continue Thursday night and Friday morning giving significant snow drifts in many areas."
A status orange warning for Connacht, Cavan, Monaghan, Donegal will come into effect on Thursday at 8pm until Friday at noon.
It reads; "Persistent snow will develop on Thursday night and will continue into Friday. Together with strong easterly winds this may lead to snow drifts."
A status orange warning for Carlow, Kilkenny, Laois, Longford, Wexford, Offaly, Westmeath, Cavan and Galway is in effect from Wednesday at 8pm until Thursday noon.
It reads; "Further snow showers tonight and on Thursday morning with significant accumulations expected."
Finally, a Status Yellow snow-ice warning is in place for Donegal, Monaghan, Leitrim, Mayo, Roscommon, Sligo, Clare, Kerry, Limerick and Tipperary. It is in effect from Wednesday 8pm until Thursday at noon.
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