A red snow and ice warning for for Munster and Leinster has been extended into Friday evening.
Two separate red warnings are in place around the country.
An earlier, single warning for the entire country has been stood down.
A status red snow-ice warning is in place for Connacht, Cavan, Monaghan and Donegal until 6.00am on Friday.
Met Éireann says sub-zero temperatures and icy conditions will continue Thursday night in strong easterly winds - with heavy snow showers and high accumulations in some areas.
While a separate, extended status red snow-ice warnng has been issued for Munster and Leinster.
The forecaster says there will be blizzard conditions Thursday night and during Friday in Leinster and Munster.
It adds that southern and eastern coastal counties are expected to receive "exceptionally high accumulations."
This alert is in place until 6.00pm on Friday.
Severe Weather Warnings Update: https://t.co/9BeK3UcAwO
— Met Éireann (@MetEireann) March 1, 2018
Members of the public have been warned to stay indoors from 4.00pm on Thursday.
— Nicole Gernon (@nicole_gernon) March 1, 2018
The red warning calls for people to take action to protect themselves and their property - with conditions expected that have not been seen since 1982.
Further snow showers are expected, while Storm Emma brings blizzard-like conditions.
All schools, colleges and third level institutions will be closed Thursday and Friday.
Full details of public transport cancellations can be found here - with no Irish Rail, Luas or Dublin Bus services operating Thursday or Friday.
The HSE has urged patients to contact health facilities before making any unnecessary journeys.
Taoiseach Leo Varadkar is warning people not to take any chances.
“In a blizzard scenario people may not even be able to see the hand in front of their face,” he said.
“It could be a total whiteout under certain conditions, so it is not the occasion to engage in daredevil activities.”
Speaking after a meeting of the National Emergency Coordination Group, he said every state resource is being put to use to ensure people are safe during storm Emma.
He urged everyone in Leinster and Munster to stay indoors between 4.00pm Thursday and midday Friday.
“We have not experienced blizzard-like conditions like this since 1982,” he said.
“But the reports from that time remind us of the serious and life-threatening conditions that can be posed by heavy snow and strong winds when they come together.”
Milk and bread rationed in Dublin. Image: Paul Quinn/Newstalk
The Defence Forces have deployed 250 army personnel and 85 vehicles in a range of tasks to support the local authorities in the past 36 hours.
Some 130 personnel were deployed on Thursday alone.
There are also an additional 250 personnel in support of deployed personnel working in barracks around the country.
The majority of tasks are in support of the HSE - ensuring that key staff can get to hospitals and to house-bound patients.
250 personnel & 85 vehicles deployed in last 36 hours, hundreds more supporting from barracks around the country. Non essential ops stood down as of 4pm, "in extremis" life & death requests only from Regional Emergency Coordination Managers #staysafe #sneachta #BeastFromTheEast pic.twitter.com/LzKoiQyI0w
— Irish Defence Forces (@defenceforces) March 1, 2018
They have also supported Temple Street Children’s Hospital in Dublin, getting key staff to work as well as hospitals in Louth, Wexford, Waterford, Cork and Kildare.
Defence Forces personnel are also deployed in support to An Garda Síochána for mobility operations - supporting local county councils to assist in clearing key transport hubs and providing meals and wheel services.
However the Defence Forces ceased conducting non-essential operations at 4.00pm Thursday, such as clearing snow and ice.
Personnel will be available for "in Extremis" situations of life and death after that time.
Meanwhile, the public is being praised for heeding the safety warnings so far.
Seán Hogan is the Chair of the National Emergency Coordination Group, which is formulating the country's response to the snow storm.
“That was the experience too in Storm Ophelia,” he said. “People listened.”
“[They] took the message on board.
“We think this is the safest thing to do. We think this is the only thing to do in fact.
“There is in between space here on this one. People in Ireland are solid sensible and doing the right thing.”
He expressed his hope that there will be no fatalities when the worst of the weather hits - and warned that anyone who ventures outside after four will be putting their life at risk.
Blizzard conditions are developing from the south as heavy snow and strong easterly winds bring snow drifts northwards over the country.
The snow showers will bring significant levels of snow accumulation with all areas at risk.
Eastern and southern coastal counties will be worst affected.
Temperatures will be as low as -4C degrees and there will be strong to gale force northeast winds.
No flights will depart or arrive at Dublin Airport from 4.00pm Thursday.
Due to continuing adverse weather conditions, Ryanair expects further flight delays and cancellations at airports today and tomorrow (Thursday 1st and Friday 2nd March 2018) and we recommend customers check the status of their flight below before making their way to the airport.
— Ryanair (@Ryanair) March 1, 2018
Shannon Airport has also shut until Saturday.
These bewildered tourists are walking around an empty Dublin city:
Additional reporting: Jack Quann