There are now more Covid-19 patients in NHS hospitals in England than during the peak of the first wave in April, new figures have revealed.
The NHS England data shows there were 20,426 patients in NHS hospitals in England as of 8am on Monday, compared to the 18,974 patients recorded on April 12.
The number of further lab-confirmed cases of coronavirus recorded in a single day in the UK also hit a new high of 41,385 as of 9am Monday, according to Government figures.
Dr Yvonne Doyle, medical director at Public Health England, said: "This very high level of infection is of growing concern at a time when our hospitals are at their most vulnerable, with new admissions rising in many regions."
The figures come amid warnings that hospitals in the South are facing a rise in pressure due to the increasing number of coronavirus patients.
Saffron Cordery, deputy chief executive of NHS Providers, said: "We know that the rate of Covid-19 admissions is rising and some trusts are reporting up to three times the number of Covid patients than at the peak of the first wave.
"This means hospitals and also ambulance services in Tier 4 areas and beyond are incredibly busy, compounded by increasing staff absences due to illness and the need to self-isolate."
Dr Nick Scriven, immediate past president of the Society for Acute Medicine, called the trend "extremely worrying" and said "systems will again be stretched to the limit".
"It is not 'just the case' of using the Nightingale hospital as there are simply no staff for them to run as they were originally intended (mini intensive care units)," he said.
"They could play a role perhaps if used as rehabilitation units for those recovering but, again, where do we find the specialist staff – the NHS simply does not have the capacity to spare anyone."
Paramedics in the capital are receiving support from other ambulance services in the South as they receive up to 8,000 999 calls each day.
London Ambulance Service described Boxing Day as one its "busiest ever days", with 7,918 callouts – up more than 2,500 on the 5,217 received on the same day last year.
Yesterday we received more than 7,000 calls. We'll take 5,500 calls on a typical 'busy' day.
Please continue to help us help you – only call 999 in an emergency. For urgent medical advice when it's not an emergency, please go to NHS111 online first: https://t.co/z1JoP2fYFE.
— London Ambulance Service (@Ldn_Ambulance) December 28, 2020
Medics remained busier than usual on Sunday, with 7,111 calls, compared with 5,411 on December 27 2019.
Dr Katherine Henderson, the president of the Royal College of Emergency Medicine, described her experience of working in a hospital on Christmas Day as one of "wall-to-wall Covid".
She told BBC Breakfast: "The chances are that we will cope but we cope at a cost – the cost is not doing what we had hoped, which is being able to keep non-Covid activities going.
"So we will stretch staff, the problem is at the moment we have a lot of staff sickness."
Professor Jackie Taylor, president of the Royal College of Physicians and Surgeons of Glasgow, told the programme London and the South East are now experiencing what Scotland went through in the autumn.
The Government said a further 357 people have died within 28 days of testing positive for Covid-19 as of Monday, bringing the UK total to 71,109.
Meanwhile, an outbreak of further positive Covid-19 cases at Manchester City led to their Premier League trip to Everton being postponed just four hours before kick-off.
More than six million people in east and south-east England went into the highest level of restrictions on Saturday, which now affects 24 million people representing 43% of the population.
Lockdown measures are also in place across the other three home nations, after mainland Scotland entered Level 4 restrictions from Saturday for three weeks, and a similar stay-at-home order is also in place in Wales.
Northern Ireland has also entered a new six-week lockdown, and the first week measures are the toughest yet, with a form of curfew in operation from 8pm, shops closed from that time and all indoor and outdoor gatherings prohibited until 6am.
Calum Semple, professor of outbreak medicine at the University of Liverpool and a member of the Scientific Advisory Group for Emergencies (Sage), described the Oxford/AstraZeneca vaccine as a "game changer" if it is approved by the Medicines and Healthcare products Regulatory Agency (MHRA) in the coming days but warned "herd immunity" through vaccination would not be likely until the summer.
Meanwhile, Downing Street and Department for Education (DfE) officials were due to meet on Monday to discuss whether schools should be kept open if tougher measures are needed, although the DfE declined to comment on the outcome.
But Cabinet Office Minister Michael Gove said the Government hopes the staggered reopening of schools in England will go ahead in January as planned.
A DfE spokeswoman added: "It is right that we follow the path of the pandemic and keep our approach under constant review."