The plan to ease Covid rules over Christmas in the UK is a "rash decision" that will "cost many lives", two leading medical journals have said.
The Health Service Journal and British Medical Journal said people might see the lifting of restrictions "as permission to drop their guard".
Cabinet minister Michael Gove has held talks on the issue with leaders in Scotland, Northern Ireland and Wales.
NI said scientific advisers would be consulted ahead of any decision.
It comes after Labour called on ministers to hold an emergency review of the plans.
Earlier, No 10 said the rules were "under constant review" but it still intended to allow families to meet up.
The prime minister's spokesman said the government had been clear that people needed to "remain cautious and vigilant" during the five days of relaxed rules from 23 to 27 December.
The BBC's Nick Eardley said one possible change being discussed was a limit on how far people can travel, but he stressed that no decisions had been taken.
It comes as millions of people in London and parts of Hertfordshire and Essex prepare to move into England's toughest tier of coronavirus rules at 00:01 GMT on Wednesday.
Meanwhile, another 18,450 cases and 506 deaths within 28 days of a positive test were reported in the UK on Tuesday, government figures showed.
In a joint editorial criticising the UK's Christmas rules, the editors of HSJ and BMJ wrote: "We believe the government is about to blunder into another major error that will cost many lives.
"If our political leaders fail to take swift and decisive action, they can no longer claim to be 'protecting the NHS'."
They stressed that demand on the NHS was increasing, and added that a new strain of coronavirus "has introduced further potential jeopardy".
Labour leader Sir Keir Starmer urged Prime Minister Boris Johnson to convene an emergency Cobra meeting to review the Christmas rules.
In a letter, he acknowledged that people "want to spend time with their families after this awful year", but said "the situation has clearly taken a turn for the worse since the decision about Christmas was taken".
At the end of November, the leaders of the four UK nations agreed to allow some coronavirus rules to be temporarily relaxed over the festive period.
Travel restrictions will be eased to allow up to three households to form a bubble and stay overnight at each other's homes.
Ahead of the latest talks, Scotland's First Minister Nicola Sturgeon said there was "a case" for tightening planned rules over the Christmas period - "both in terms of duration and numbers of people meeting".
She said coming to a four nations agreement "would be preferable", but added: "If that is not possible then of course we will consider within the Scottish government what we think is appropriate."
Wales' First Minister Mark Drakeford said he would not "lightly" put aside the agreement the four nations have reached, while Northern Ireland's health minister would not speculate on potential rule changes ahead of the call.
According to a YouGov poll, a majority of people (57%) in Great Britain believe the relaxation of coronavirus restrictions over Christmas should be scrapped.
Some 31% said the easing should go ahead as planned, while 12% said they were unsure.
When the government announced the relaxation of rules for Christmas, it was hoped cases would be falling right up to the festive period.
It was mid-lockdown and with the new tougher system of regional tiers in the pipeline, the hope was that the virus could be contained.
That has not turned out to be the case - hence the moving of London and some of the surrounding areas into tier three.
As always, the bottom line is the risk to the NHS - so it's worth pointing out that for all the pressure at the moment hospitals still have more beds free than this time last year.
The full impact of the festive relaxation is, of course, impossible to predict. The UK's chief medical adviser Prof Chris Whitty has called it a "modest" relaxation - after all, in tier three areas hospitality will still be closed for all but takeaways.
The judgement that has been made is that the benefits outweigh the costs.
Allowing families to come together will be an important boost after such a difficult year, the government believes. What is more, there was a fear the public would just ignore pleas not to mix.
But it clearly comes with risks - that's why the public is being asked to exercise caution.
If the UK's Christmas plans are not changed, BMJ editor in chief Fiona Godlee said "we will have people sitting in ambulances, we will have people in corridors" as hospitals become overwhelmed with a surge in Covid patients.
Speaking to BBC News, she said: "On the current trend, if nothing is done, by New Year's Day there will be as many people in hospital with Covid-19 as there were at the peak of the first phase in April.
"That's even without the Christmas relaxation - so if you add that on top, and then on top of that the winter pressures that we always see in the NHS at winter, you will see a worrying scenario of people not being able to get the care they need."
She also said England's tiered system is "not succeeding in what it set out to do", as case numbers have continued to increase in some areas in the top tiers.
A review of which areas of England are in which tier is scheduled to take place on Wednesday.
It has already been announced that some 10.8 million people across London, Essex and Hertfordshire will join tier three on Wednesday, bringing the total number of people living under the toughest restrictions to 34 million people - or 61% of England's population.
Under tier three - very high alert - rules, pubs and restaurants must close, except for takeaway and delivery, and indoor entertainment venues such as theatres, bowling alleys and cinemas must remain shut.
In other developments:
- Mass Covid testing of secondary school pupils in England is to be greatly increased in January, in an attempt to reduce the number of children being sent home
- Greenwich Council in south-east London has withdrawn its request to schools in the area to move classes online amid a rise in Covid cases, after being threatened with legal action by the government
- The higher numbers of deaths seen in the UK in recent weeks may be starting to fall, figures suggest
- There were 819,000 fewer workers on UK company payrolls in November than at the start of the pandemic, official figures show, with hospitality the worst-hit industry.
- VACCINE HESITANCY: Why do some people have concerns about taking a new coronavirus vaccine?
- BRAND NEW THE VICAR OF DIBLEY: Geraldine returns to offer her thoughts about lockdown and social distancing