Health Minister Robin Swann has said it is likely the Omicron Covid-19 variant is already in Northern Ireland.
The Omicron variant, which has been labelled a “concern” by the World Health Organisation, has been detected in England and was linked to travel in southern Africa.
No cases have yet been notified in Northern Ireland or the Irish Republic.
However, Republic of Ireland Minister for Health Stephen Donnelly said it was “likely” Omicron is already present.
In a statement to Stormont’s MLAs on Monday, Mr Swann said although there is “limited evidence” of the impact of the new variant, there is still the potential it could be resistant to vaccines and more transmissible.
“As yet it is unclear if it would be more serious in terms of the clinical impact,” he stated.
“At this particular moment, there have been no confirmed cases of the Omicron variant identified in Northern Ireland, but it is highly likely that this position will change in the coming days.
“The Public Health Agency (PHA) is undertaking detailed risk assessments of some returning travellers from red-listed countries and is advising on any immediate public health actions which are required to slow the introduction of this variant and to limit its spread in Northern Ireland.
“In light of the cases identified in England and Scotland it is to be expected that there may already be cases of the variant in Northern Ireland.”
Mr Swann also announced a tightening of restrictions for international travellers arriving into Northern Ireland.
From 4am on Tuesday, anyone arriving into Northern Ireland from non-red list countries, including those who are fully vaccinated, will be required to self-isolate and take a PCR test before the end of day two.
The Health Minister said the restrictions will be reviewed in three weeks.
“I recognise that the measures I am announcing today will have consequences for individuals, their families and the local economy,” he told the Assembly.
“However, it is essential that we follow the approach that has been announced for the rest of the United Kingdom in order to reduce the risk of a potentially even greater and more serious wave of infection than we currently face.
“The position in the Republic of Ireland will also be kept under close observation.
“I sincerely hope that the scale of the transmissibility advantage of the new variant is not as large as feared and/or that the symptoms are more moderate than the delta variant, particularly for the most vulnerable.
“Until we know more about the characteristics of the new variant it is not acceptable to take the risk with the health of our people, and we need to take action urgently.
“It should be stressed that although the Omicron variant may reduce the effectiveness of the current vaccines, it remains very likely that vaccination will continue to protect against severe illness from Omicron as it does against other variants.”