The First Minister has confirmed the current conditions mean Wales has met the criteria in the new traffic light Coronavirus Control Plan to move to alert level 4.
The new restrictions will apply to all of Wales.
The First Minister urged everyone who can to work from home, saying it is one of the most important contributions we can all make to controlling the spread of coronavirus and saving lives.
Mark Drakeford said:
"We are seeing levels of coronavirus in some parts of the country that we haven’t experienced at any point before in this pandemic. This pandemic is putting our NHS under intense and sustained strain.
"There are more than 2,100 people with coronavirus symptoms in our hospitals – equivalent to 5 general hospitals fully occupied by people with coronavirus.
"This has been such a long and difficult year. We need to take this action to save lives and control the spread of this awful virus."
The 4 UK governments met today to confirm the common arrangements for the 5-day Christmas period. Joint advice will be published later today.
In Wales, the position will be that only 2 households should come together to form an exclusive Christmas bubble during that period.
The First Minister added:
"A smaller Christmas is a safer Christmas and a shorter Christmas is a safer Christmas.
"The fewer people we mix with in our homes, the less chance we have of catching or spreading the virus.
"None of us wants to be ill this Christmas. And we don’t want to give coronavirus to our close family or friends."
The alert level 4 restrictions for household mixing, staying-at-home, holiday accommodation and travel will come into force after the 5-day Christmas period on December 28.