Louise Wallace, the county's new director of public health, told a briefing on Wednesday that the new coronavirus variant was likely to have reached the county and said any plans to meet with those from other households should be postponed.
"Nobody wants to get Covid for the New Year," she said, "and I really, really hope people do enter the New Year fit and well by taking responsibility for themselves to not spread this virus anymore.
"Unlike Christmas day, there are no restrictions relaxed over New Year so please do not have people at home in parties or gatherings if you do not live with them.
"At this point in time the most important thing is to get back to basics on hand-washing regularly, wearing face coverings and maintaining social distance."
North Yorkshire has today moved into Tier 3 restrictions with a ban on social mixing indoors and most outdoor spaces, except for support bubbles.
The ban on mixing includes private gardens, however, groups of up to six people can meet at parks, beaches, public countrysides and gardens, allotments, the grounds of heritage sites, outdoor sports facilities and playgrounds.
Pubs, restaurants and cafes must also shut - unless for takeaway or collection.
North Yorkshire Police's chief inspector Charlotte Bloxham said the county's new tier status should act as a "wake up call" for people and warned those who flout the rules risk fines.
Speaking on Wednesday, inspector Bloxham said: "To those who continue to ignore the regulations, I hope that today’s announcement acts as a wakeup call for you.
"If you do choose to disregard the rules, not only will this situation continue and we run the risk of even tighter restrictions, but you also risk picking up a £200 fine and even worse, the virus itself.
“As throughout this pandemic, I’m sure that the majority of people will understand why the tighter restrictions have been introduced and will act responsibly to protect the most vulnerable among us."
By Jacob Webster, Local Democracy Reporter