Wales and Scotland are also introducing new measures.
Today sees the introduction of a number of new Covid-19 measures in Northern Ireland.
RTÉ reports that the new rules apply to indoor events, nightclubs and social mixing between households.
From today, all nightclubs in Northern Ireland will close while indoor standing events are not permitted to go ahead.
Up to six people can meet in indoor hospitality settings, though socialising is to be reduced to three households.
10 people are allowed to sit together in pubs, bars and restaurants if they are all from the same household.
Meanwhile, in offices and other public premises, a social distance of two meters will be put into place.
The new restrictions come after Northern Ireland saw a 55% increase in positive Covid-19 cases compared to this time last month.
In the week leading up to Christmas Eve, Northern Ireland recorded 17,861 infections. There were 18 deaths from the virus.
Elsewhere in the UK, Scotland and Wales are implementing further restrictions. Nightclubs in Scotland must now close, while indoor hospitality venues that only serve alcohol must now operate table service. Additionally, a one-meter social distance rule must now be introduced in bars, restaurants, theatres and museums. Socialising is also limited to three households.
In Wales, a maximum of six people are permitted to met in indoor hospitality settings and a two-meter social distancing rule must now be enforced in public premises and offices. Nightclubs must now close and there are also caps on numbers at indoor and outdoor events.
As for England, Prime Minister Boris Johnson will soon be briefed on the impact of Covid-19 restrictions on the NHS. No decisions have yet to be made.
In Ireland, Christmas Day saw a record number of Covid-19 infections. 13,765 cases were reported, which is the highest single-day figure for infections in the country since the start of the pandemic.