Health Minister Stephen Donnelly has said the UK variant of Covid-19 is "unlike anything we have dealt with in this country so far."
He also gave a message to everyone, particularly the most vulnerable.
Speaking on his way into Cabinet at government buildings, Mr Donnelly told reporters the new variant is "far more contagious."
He said: "The situation now is to my mind the serious it has been since the start of this.
"We got more evidence last night, it's still early evidence but more evidence to the prevalence and the rapid spread of this UK variant.
"This UK variant is unlike anything we have dealt with in this country so far.
"We've seen what it's doing in the UK and what it's doing in countries right across Europe.
"We know it's here, the only question is to what level it's here.
"It's far more contagious than anything we have dealt with so far.
"So regardless of what Cabinet decides today everything is focused around one message which is stay at home."
He added: "And people who are vulnerable to this virus my message is think back to March, April, May.
"Think back to how careful everybody was and everybody became...think like that again but remember this virus is more contagious than that virus, this variant is more contagious, that's where we've got to go just like we did in March, April and May.
"We've got to slow down and look out for each other now and slow this thing down."
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