Emergency hospital consultants in Wales have written to the first minister claiming safety is being compromised “to an unacceptable degree”.
The group said they recognised funding constraints but said both NHS Wales and the social care sector were “severely and chronically under-resourced”.
Figures showing how A&E departments and the ambulance service coped in December are due out on Thursday morning.
The Welsh Government has been asked to comment.
It said it did not dispute the effort which had gone into winter planning but “unfortunately our experience from the clinical front line is that these plans have fallen well short of what was required to maintain adequate care for our patients”.
The letter from the consultants in Wales goes on to say: “We have neither sufficient staff nor sufficient beds (in either acute hospitals or the community) to cope with the needs of an ageing population”.
‘Staff in tears’
They said emergency departments in Wales “in some ways” were worse than in England.
Examples given include staff arriving for work to find patients in the emergency department who were there the previous day and “multiple” staff in tears because they feel they cannot deliver the care patients need.
One of the signatories, Dr Tim Rogerson, a consultant in emergency medicine at Newport’s Royal Gwent Hospital, said: “We’re on our knees as far as emergency care [is concerned].
“We have patients coming into emergency departments that are already full.”
He added: “There’s good evidence that if patients are seen in emergency departments which are crowded, that are full, their treatment is delayed.
“That can actually cause an increase in the length of stay, it can make their illness more severe and in some cases it can cause death, so for safety and patient care we’re very, very worried.”
The consultants’ letter calls on First Minister Carwyn Jones to address issues “as a matter of urgency”, including reviewing the number of beds available for acute care and a “significant increase” in funding for social care.
December has already been reported to be the highest month on record for life-threatening “red calls” to the ambulance service.
NHS Wales chief executive Dr Andrew Goodall and Health Secretary Vaughan Gething have already apologised for postponed routine operations due to “exceptional” demand.
On patient care, Dr Goodhall said: “I think there will be times when the patients are not receiving the care or the access that we would want to move them through the system and it is absolutely true that there will have been some very difficult shifts and periods for staff.”
He added: “This has been a very challenging period for us and that’s true on pressures on staff but I want to recognise the NHS is busy all year around – we have one million A&E attendances a year.”
The ambulance service saw a rise of almost 50% in the number of red calls it attended on New Year’s Eve and out of hours services were 30% busier on some days.
But patterns have been difficult to estimate with increases at different times to those seen last year.
“There are unpredictable moments,” said Dr Goodall. “Even at this very pressurised time of year – in the last few days, the proportion of older people arriving in our A&E units was one of the lowest on Saturday and one of the highest was over the last couple of days.”
NHS Wales said it had freed up an extra 400 beds over the winter – the equivalent of a new hospital.
But Dr David Bailey, chairman of the British Medical Association in Wales, said the lack of spare capacity in hospitals was an issue.
He said: “You can plan for spikes – some of the spikes may be bigger than you expect and we’ve some of the issues with flu this year.
“But actually, we get issues with flu every year and more people get sick in winter every year. None of these are unexpected but we need more capacity.
“The problem is the NHS is not really set up to cope with spikes in demands and every spike takes three times longer to recover from.”
Dr Graham Shortland, medical director at Cardiff’s University Hospital of Wales said it had managed to free up beds ahead of the winter period but flu cases had added to pressures.
“The key thing is flow,” he said.
“Can we reduce demand through the front door? Can we process patients more quickly in this department?
“Can we move them on to the ward and ultimately move them back quickly, home or to the care of their family?”