A number of homes are without power due to severe weather conditions causing damage to the network, Northern Ireland Electricity (NIE) said.
A severe weather warning has been issued for three counties.
The Met Office has said parts of counties Antrim, Down and Armagh can expect snow and ice between 15:00 GMT on Thursday and 04:00 on Friday.
The amber warning is the second highest level that can be issued by the Met Office and means there is a risk of travel delays and road closures.
Other counties are under a lesser, yellow-level warning.
Snow has been falling across many areas on Thursday night and it is expected to become more heavy and persistent towards the east coast.
The Met Office is warning of "atrocious" travel conditions, especially over higher ground.
Between 4cm and 8cm of snow is expected away from coastal areas, with between 10cm and 20cm over higher ground.
The yellow warning for the rest of Northern Ireland lasts from 07:00 GMT on Thursday until 14:00 on Friday.
A number of roads have been closed due to treacherous conditions, including Church Road in Holywood, County Down.
The Strangford ferry has been suspended and some bus services disrupted.
Belfast International and Belfast City Airports have tweeted that there may be flight disruption due to the weather conditions.
The Police Service of Northern Ireland (PSNI) is advising drivers to take extra care, especially on roads that may not have been gritted.
Road gritting services have been disrupted by industrial action in a dispute about pay.
Stormont's Department for Infrastructure said some gritting would be done but the service would be reduced.
It has said it will "prioritise the areas at greatest risk, such as high ground".
It added that it had "external snow clearance contractors available to treat areas such as the Glenshane Pass if we need to do so".
Road maintenance workers in the Unite and GMB unions have protested over a pay bonus, which they argue should be given to all staff.
The department said it was "committed to resolving this dispute" but called for a "derogation for winter service for the next few days".
The government information service NI Direct has posted a listed useful emergency contact numbers for those affected by the snow and ice.
Armagh, Banbridge and Craigavon Borough Council has announced that all council facilities will close until midday on Friday due to the snowfall.
In the Newry, Mourne and Down District Council area all forest parks have been closed with further closures possible on Friday.
The Education Authority warned that its school transport service may be disrupted on Friday morning, particularly in rural areas.
In the Republic of Ireland, snow and ice warnings have been issued through Thursday and Friday.
The second highest level of warning has been issued for for snow across 13 counties in Ulster, Connacht and parts of Munster and Leinster.
The Irish weather service Met Éireann has warned of significant snow and ice in some areas.
In the Republic, National Emergency Coordination Group chair Keith Leonard said there will be major disruption across the road network on Friday.
Mr Leonard added that schools may close on Friday, but it will be decided by principals based on the local weather conditions.