A surge in coronavirus cases in the UK is of "extreme concern", a health boss says, as a record number of cases was reported for the second day running.
On Tuesday, 53,135 new Covid cases were recorded as well as 414 more deaths within 28 days of a positive test.
Not all data was reported in full over the Christmas period, leading to a lag in some data, but Public Health England said there had been a "real increase".
The health secretary said the NHS was facing "unprecedented pressures".
Ahead of an announcement on any changes to England's tier restrictions on Wednesday, Matt Hancock added in a tweet: "We must suppress this virus to protect our NHS & save lives until the vaccine can keep us safe."
Hospitals in England and Wales are now treating more Covid patients than at the peak of the first wave in April.
Dr Susan Hopkins, senior medical adviser at PHE, said: "We are continuing to see unprecedented levels of Covid-19 infection across the UK, which is of extreme concern, particularly as our hospitals are at their most vulnerable.
"Whilst the number of cases reported today include some from over the festive period, these figures are largely a reflection of a real increase."
Dr Hopkins said it was "essential, now more than ever" that people follow social distancing rules to help drive infections down and protect the NHS and vulnerable people.
It comes a day after more than 40,000 daily virus cases were announced for the first time in the UK, although it is thought infection rates were higher earlier in the year, before mass testing.
In Wales' Brecon Beacons beauty spot, police have had to turn away visitors from as far away as London - which is under "stay at home" tier four rules.
People in Scotland have been urged to stay at home and not celebrate Hogmanay with other households.
And in Northern Ireland a top doctor has warned a third surge of Covid cases is expected in mid-January, in part driven by the spread of a new coronavirus variant.
There is no shying away from these very big, record-breaking figures and the strain they put on the NHS.
Many hospitals in the UK are already caring for more people with Covid than during the first wave and the situation looks set to get worse, not better - at least in the short term.
New infections are rising rapidly, which will pile on even more pressure on busy wards in the coming weeks.
Although much of the UK has introduced tougher Covid restrictions, it is not clear yet if they will be enough to help drive infections down, or at least hold them at manageable levels.
There is a new variant of Covid that has been spreading more readily, which complicates things.
And we are yet to see what the permitted (and banned) Christmas socialising will do to the figures.
The NHS is coping and open for business, but medics fear it being tested to breaking point.
A scientist advising the government has said "decisive" national action is needed to tackle the spread of the virus across the UK and prevent a "catastrophe" in the new year.
Prof Andrew Hayward, a member of the government's New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said the new variant meant the UK was entering "a very dangerous new phase of the pandemic".
He told BBC Radio 4's Today programme the "50% increase in transmissibility" of the new variant means restrictions that worked before "won't work now" so England's tier four restrictions, "or even higher than that", were likely to be needed.
"I think we're really looking at a situation where we're moving into near lockdown," he added.
Tier four - England's toughest level of coronavirus restrictions, currently in place in parts of east and south-east England - includes a "stay at home" order and the closure of non-essential shops.
Prof Hayward, a professor of infectious disease epidemiology at University College London, said he thought schools would have to return "maybe a little bit later" but that having schools open would mean "we're going to have to have increased, strict restrictions in other areas of society to pay for that".
The prime minister's official spokesman said the government was "still planning for a staggered opening" of secondary schools after Christmas but it was keeping this under constant review.
Members of the armed forces will be on standby to help roll out mass testing to secondary schools and colleges in England from next month.
Another epidemiologist and member of Nervtag, Prof Neil Ferguson, said the new coronavirus variant had "undoubtedly" made the situation "considerably more difficult".
He told BBC Radio 4's The World at One programme that it had given the government "even less wiggle room" in trying to keep control of the virus while maintaining "some semblance of normal society".
Preliminary research released on Tuesday suggested the new variant of the virus was no more harmful in terms of causing hospitalisations and deaths.
Researchers found no significant difference in terms of mortality or morbidity when they compared 1,769 people infected with the new variant versus 1,769 who had "regular" or "wild type" of Covid.
Hospitals in Wales, Scotland and the south of England have reported rising pressure on their services as the number of Covid patients increases, with health officials warning they are at risk of becoming overwhelmed.
Southend University Hospital in Essex has asked staff to cancel holidays to help treat its high number of Covid patients.
Emergency medicine consultant Simon Walsh, who works in north-east London, said staff were working in "major incident mode" in many hospital trusts across south-east England.
He said they were dealing with "queues of ambulances outside many emergency departments" and some were considering setting up triage tents - normally reserved for major incidents like terror attacks - outside hospitals.
Staff at Queen's Hospital in Romford, east London, are being encouraged to take on additional shifts, and some Covid patients are being cared for in ambulances outside the hospital.
The hospital's chief medical officer, Magda Smith, said London's NHS was under "significant pressure" and "we are opening more beds to care for the most unwell patients".
Prof Steve Hams, chief nurse at Gloucestershire Hospitals NHS Foundation Trust, said patient numbers were becoming "increasingly challenging" and staff were becoming "increasingly exhausted".
In a new year message to staff recorded at a vaccination centre, NHS England chief executive Sir Simon Stevens said Covid-19 meant 2020 had probably been "the toughest year most of us can remember".
He said the "the biggest chink of hope" for 2021 was that by late spring he expected the NHS to have offered vaccinations to all vulnerable people.
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