The much-anticipated Siberian storm arrived yesterday, bringing dry snow and bitterly cold winds. Temperatures today will feel as low as -10C.
The Met Office has warned that frequent and occasionally heavy snow showers are expected to continue through much of Thursday, with Belfast, Armagh and Newry worst affected.
Further delays and cancellations to all forms of transport are likely and roads may become blocked by deep snow and some rural communities might become cut off.
Interruptions to power supplies and other services such as telephone and mobile phone networks could also occur.
There is current delays and cancellations to arrivals and departures at Belfast City Airport and Belfast International Airport and more than 250 schools have been closed.
Parks and playgrounds in Belfast have been closed. Prison visits have been halted.
Vehicle testing has been disrupted and hospital outpatient clinics in the Southern Health and Social Care Trust cancelled.
The border counties of Armagh and Down have been worst affected with some of the main roads including the M1 motorway reduced to one lane in parts.
"Driving conditions in counties Armagh and Down are particularly difficult and we are focusing most of our efforts in those areas at present," said Simon Wells from the Roads Service.
A spokesperson for Flybe, which operates out of Belfast City Airport, said: "Due to the adverse weather that is being experienced and forecasted over the next few days with the potential to impact travel across large parts of the UK, airports may either close temporarily or restrict the number of arriving and departing flights.
"Flybe, like every airline, has minimum acceptable weather conditions in which we can safely operate. Please be assured that we will be doing our best to ensure that flights operate as normal, taking into consideration any adverse weather conditions. The safety of our passengers and crew remains our number one priority at all times."
Translink has asked commuters to check travel updates on its website before travelling.
SDLP MLA Sinead Bradley has urged people to exercise caution as adverse weather batters local communities.
The South Down MLA has also called on business owners to consider the safety of their staff as conditions worsen.
She said: “The weather has deteriorated very quickly and we’re now in the middle of an amber warning from the Met office.
“As conditions worsen, and are set to decline throughout the day, it’s important that local people exercise caution. People need to start planning a route home now and business owners should reflect on the need for staff to be present at all. If alternative arrangements can be put in place, they should.
“For those already at home, I would encourage them to look in on elderly or vulnerable neighbours throughout the day. This is a time for community spirit to shine through and if you can do anything for a neighbour, please do."
Sinn Féin MP Elisha McCallion called for joined-up planning for weather warnings across the island.
The Foyle MP said; “In light of the severe weather across the island at the moment, it makes sense for us to plan on an all-island basis.
“On Wednesday a red alert was issued across the entire 26 counties meaning there was threat to life as a result of the severe weather but at the same time a yellow alert was issued in the Six Counties.
“How can such a serious alert be in place in Burnfoot in County Donegal but not be in place several miles away in Derry?
“Weather does not recognise borders and neither should weather planning systems.
“We should have a joined-up emergency planning service across the island to deal with severe weather situations to ensure we are prepared in the best way to keep people north and south safe.”