The majority of Scotland will be put into a full lockdown from Boxing Day, Nicola Sturgeon has announced.
The First Minister said mainland Scotland will be moved into level four for three weeks amid fears a new variant strain is accelerating the spread of coronavirus.
Orkney, Shetland and the Western Isles will be moved from level one into level three.
The relaxation of the coronavirus rules over the festive season have also been scaled back to Christmas Day only.
Schools will also remain closed for most pupils until January 18, with a week of home learning from January 11.
Up to three households in Scotland were initially allowed to gather indoors between December 23 and 27.
However, the First Minister announced on Saturday at a Scottish Government briefing that the five-day window was now being reduced to December 25 only.
A strict travel ban has also been put in place over the holidays, with cross-border travel between Scotland and the rest of the UK not permitted.
Sturgeon said: “Unfortunately, and I am genuinely sorry about this, that ban will remain in place right throughout the festive period.
“We simply cannot risk more of this new strain entering the country if we can possibly avoid it.
“That means people from Scotland not visiting other parts of the UK, and vice versa.
“Cross-border travel for all but the most essential purposes is not permitted.”
Christmas holidays for most Scottish pupils have been extended to January 11 and the majority will begin the new term studying from home until at least January 18.
The First Minister said schools will reopen as currently scheduled for some pupils, such as the children of key workers and the “most vulnerable”.
The First Minister said the new strain may be up to 70% more transmissible than the old variant and could increase the R number by 0.4.
She said that 17 cases of the new strain have been recorded in Scotland.
Sturgeon warned: “But I think we have to be realistic that that is likely to be an understatement of its true prevalence right now.”
Earlier on Saturday, Boris Johnson cancelled Christmas for millions of people across London and south-east England.
The Prime Minister announced that from Sunday areas in the South East currently in tier three will be moved into a new tier four – effectively returning to the lockdown rules of November.
The rest of England will also see the Christmas “bubble” policy – allowing up to three households to meet up over the holiday period – severely curtailed, applying on Christmas Day only.
The move came after scientists on the Government’s New and Emerging Respiratory Virus Threats Advisory Group (NervTag) concluded that the mutant strain identified by Public Health England – known as VUI2020/01 – was spreading more quickly.
Sturgeon said “we do now face a very serious situation”.
She added: “It is, in fact, probably the most serious and potentially dangerous juncture we have faced since the start of the Covid pandemic in February and March.”
1/ I know this is tough. But this new virus strain is spreading much faster, and so we must act quickly to stop it taking hold. That means even tighter restrictions through January to prevent the serious situation currently faced by places like London & save lives.— Nicola Sturgeon (@NicolaSturgeon) December 19, 2020
Sturgeon later tweeted: “And while it’s hard to see it right now, the light at the end of the tunnel is still there.
“With every day that passes, more people are being vaccinated. We will get through this – but as we do, let’s continue to love and look out for each other.”
In response to the change of measures, Scottish Conservatives leader Douglas Ross said: “Families across Scotland will be devastated at these new measures, especially so close to Christmas.
“However, given the rapidly increasing spread of the virus across the UK, and until our scientists know more about the transmission of this new variant, it is understandable why these restrictions are necessary at this time.
“None of us want this, but these sacrifices will save lives.
“We would expect the Scottish Government to ensure a return to regional levels of restrictions as soon as it is safe to do so.”
Scottish Liberal Democrats leader Willie Rennie has called for schools to be closed next week.
He said: “When the science speaks in such stark terms, the leadership of the country must listen and act.
“Shutting down mainland Scotland for three weeks will have a great impact on people’s lives, but it is the response that is necessary to match this new threat.
“However, the Scottish Government should act earlier by closing schools next week.
“The new strain of the virus is already here and pupils and teachers who are infected in school next week could pass it onto vulnerable relatives on Christmas Day. Let’s be safe and close the schools early.”
Meanwhile, Scottish Labour leader Richard Leonard added: “The Scottish Government must make decisions based on public health advice and solid evidence.
“To win public confidence behind this significant tightening of restrictions requires persuasive evidence to be published, transparency and openness, and a substantial rise in testing, otherwise not only will there be disappointment there will be a heightened risk of non-compliance.”
The mainland lockdown from Boxing Day will see shops miss out on an estimated £135m for each week they are closed, the Scottish Retail Consortium has said.
Non-essential shops, restaurants and pubs will have to close while the restrictions are in place, although takeaway food will be permitted.
David Lonsdale, SRC director, called for additional financial support for shops and an extension of business rates relief into 2021-22.
He said: “We recognise that government has difficult decisions to make and the situation with the pandemic is fast moving, but this hugely disappointing news rounds off a torrid year for Scottish retail and is a further hammer-blow to non-food stores who have already borne so much during this crisis.
“Retailers in Scotland have invested over £40m thus far making stores Covid-secure for customers and staff, and Sage’s advice has said throughout that closing non-essential retail has a minimal impact on the spread of the virus.
“The consequences of this move could be severe. This decision comes only a week after the end of the local lockdowns in west central Scotland and slap bang in the middle of peak trading which so many are depending on to power their recovery and tide them over the leaner winter period.
“Faced with this news – and the prospect of losing £135m each week in revenues during the lockdown – many stores will be in serious difficulty.
“Many could be lumbered with unsold pre-Christmas stock which will be difficult to shift in the absence of the usual Boxing Day and New Year discounted sales events, adding to cash flow woes.
“All of this will have implications for the survival of shops, for retail jobs and the vitality of our retail destinations.”