Many of the most seriously ill patients are waiting for hours on trolleys and in corridors as the NHS struggles to find them beds, BBC research shows.
Nearly a quarter of patients admitted on to wards during December and January in England faced delays of more than four hours before a bed could be found.
It has created a backlog outside hospitals with patients brought in by ambulance facing long waits too.
Experts warned there was "little in the tank" to cope with the coronavirus.
There is mounting concern that the spread of the virus will lead to a pandemic with mass outbreaks in the UK.
The BBC research – based on analysis of NHS England data – found the delays faced by some of the frailest and sickest patients have risen sharply this winter.
The Royal College of Nursing said its members were being forced to provide vital treatment, such as giving oxygen and putting patients on drips, in corridors and side rooms. It said this was unacceptable and undignified, putting patients at risk.
NHS England said rising demand was creating challenges, but added extra money was being invested which would help hospitals recruit staff and cut waiting times.
A spokesman praised staff for their hard work, adding they had "pulled out all the stops".
'I spent six hours on trolley at 93'
Kate Milsom is one of the many patients who has faced delays.
She is 93 and was taken to London's Hillingdon Hospital in January after falling at home.
The ambulance came quickly, but when she arrived at the hospital there was a long wait to be seen.
She spent more than six hours on a trolley in a corridor – much of the time with the paramedics who had brought her in.
"I was in pain. I had broken my hip before so was really worried.
"The staff were nice… but they were just so busy."
She was eventually found a bed in a bay and was able to go home the following day.
The trust said it could not comment on individual cases but acknowledged the busy nature of the hospital meant some patients faced long waits.
It said staff were working hard to keep these to an "absolute minimum" and all patients were monitored to keep them safe.
What the BBC research has found
It is already widely documented that A&E units have struggled this winter, missing the four-hour target by a record margin.
The new BBC analysis looked at waits in England before and after A&E.
It showed 199,000 patients had four-hour "trolley waits" after being seen in A&E before a bed could be found.
That is more than two times higher than the numbers seen four years ago.
In some hospitals half of patients had waited more than four hours.
Another 130,000 patients brought in by ambulances were left waiting at least 30 minutes before they could be handed over to hospital staff – one in seven of all those brought in over the two-month period.
Similar pressures are being seen in other parts of the UK, but because of the way figures are collected direct comparisons cannot be made.
The RCN said the situation had got so bad that many hospitals had started deploying nurses to work in corridors, providing treatments such as oxygen and antibiotic drips to patients.
RCN emergency care association chairman David Smith said: "It is not what we want for our patients – it is not dignified and obviously safety is a concern.
"We do our best to make sure they are comfortable and react if they deteriorate. But it is really upsetting for nurses to have to see patients like this."
The implications for a pandemic
The coronavirus outbreak could not have come at a worse time.
The winter has been the most challenging for a generation for the NHS.
The World Health Organization has said governments across the world should prepare for a pandemic – defined as when the virus is being transmitted easily in many countries.
There are signs it is spreading, with significant outbreaks reported in Italy, South Korea and Iran.
There have only been 13 cases in the UK so fRead More – Source