A top cardiologist heaves oxygen cylinders into ICU. Gynaecologists and physiotherapists volunteer for nursing shifts. And surgeons, whose regular work has been upended by Covid-19, help turn unconscious, intubated patients hovering between life and death.

As the second wave of the pandemic gathered deadly momentum, staff in Britain’s NHS painted a picture of a system close to buckling, particularly in London, with all hands required on deck. The government’s chief scientific adviser, Patrick Vallance, on Wednesday described the situation in some hospitals as “like a war zone”.

In the worst affected areas, adult patients stricken with the virus are taking over all available departments — from endoscopy to children’s wards. Frazzled doctors and nurses, stretched to the limits, said they have found stamina to carry on mainly by hauling together.

“We are at a breaking point,” said Amina Ibrahim, an operational department practitioner at St George’s hospital in Tooting, south London, who in normal times would be attending to patients undergoing surgery. In these far from normal times, she will soon begin her second year on the frontline of the pandemic.

Like many of her colleagues, Ms Ibrahim has gone almost without leave since coronavirus first started spreading last year. “As they say, you have to set yourself on fire to keep others warm. A lot of the NHS are setting themselves on fire to keep everyone else warm,” she said.

Last week, the wards in St George’s were a few beds short of being completely full and there were insufficient staff to man much more than that.

When government officials warned that the NHS was at risk of being overwhelmed, they were pointing to a scenario that is now close to playing out. Medical practitioners in hospitals from Wales to Norfolk say these are the toughest days since the start of the pandemic — significantly worse than what they experienced last year. Already overrun, some hospitals have been forced to send incoming patients elsewhere, while the “nightingale” emergency hospitals constructed at speed last year stand largely unused for want of staff.

On Thursday, there were 38,676 people in hospital with Covid-19 across the UK. Of these, 3,953 were receiving ventilation in intensive care, where there would normally be a ratio of one to one nurse to patient, but in some places it is one to six, according to several front line doctors. During the past week, 8,565 people were reported to have died within 28 days of a positive coronavirus test, a 14 per cent increase from the previous week.

The NHS’s capacity is not only being challenged by the number of critically ill patients, but also by a chronic shortage of nurses to care for them. The number of vacant positions across England stands at 38,000, according to the Royal College of Nursing, despite the recruitment of 13,000 in the past year, according to the government.

In London, several NHS officials said these pressures have been exacerbated by significant numbers of nurses and auxiliary staff, such as porters and cleaners, from EU countries leaving the UK. Everywhere, hospitals have also been under strain as a result of staff falling victim to the virus, or having to self-isolate at home.

“We have lost a lot of nurses,” said Ms Ibrahim, explaining that in her hospital several from Spain, Ireland and Italy went home last year. “You have heart doctors working as nurses. Everyone is working as nurses. It has taken all of us to help,” she added.

Last week, the NHS reopened the emergency register to take on nursing students who have yet to complete their training.

As well as London, some of the worst hit areas during the second wave of the crisis have been in south-east England, where a faster-spreading mutation of the virus first took hold.

But there are signs that the north is also overwhelmed. This week the Alder Hey Children’s Hospital in Liverpool, opened its doors to adults with the virus after nearly all critical care beds at the Royal Liverpool and Aintree hospital were reportedly taken.

Dr Simon Barry, consultant respiratory physician at the University hospital of Wales in Cardiff, said that unlike during the first wave of the pandemic, when there was an expectation that hospitals would be overrun by Covid-19 patients and few people were turning up with other problems, this time normal demand had continued.

Hospitals were also unable to discharge patients back to care homes or their own homes where they require carers even after they recovered, said Dr Barry. “That is what is crucifying hospitals. Plus there is more Covid than in the first wave, and there are far more people coming in the front door (with other ailments).”

At nearby Newport, which is among the hardest-hit towns in Wales, St Joseph’s hospital is struggling as a result.

“The second wave has been a hundred times worse,” said Dr Sara Fairbairn, a respiratory consultant. “What has been remarkable,” she added, “is that we are all exhausted and tired but everyone stands up to the plate. Everyone is doing their best to keep the system afloat.”

Until now adrenalin had kept staff going, she said, adding that the effects of the crisis on their mental health would show up later.

NHS staff fear that next week will prove even more of a challenge than this one. But they held out hope that soon after there would be some reprieve, with a decline in admissions reflecting slowly declining infection rates since lockdowns were enforced again. “We are a little broken, but we are not beaten,” said Ms Ibrahim.