One in four patients in England had to wait more than an hour to be handed over from an ambulance to A&E last week, drastically below government targets.
Nursing leaders warned the NHS is “dangerously close to overheating completely” and said the figures suggested there was “absolutely no slack in the system.”
NHS England data shows a total of 16,379 handover delays of more than an hour were recorded across hospital trusts last week.
NHS trusts in England have a target of 95% of all ambulance handovers to be completed within 30 minutes, with 100% to be completed within 60 minutes.
Among those trusts reporting at least 500 ambulance arrivals last week, the highest proportion of patients waiting more than an hour to be handed over was 58% at both University Hospitals Bristol & Weston (381 out of 655 patients) and Gloucestershire Hospitals (345 of 595).
This was followed by Northern Lincolnshire & Goole at 53% (311 of 590 patients), University Hospitals of Leicester at 52% (446 of 865), University Hospitals of North Midlands at 51% (333 of 651), Shrewsbury & Telford Hospital at 50% (271 of 540) and University Hospitals Dorset also at 50% (409 of 817).
Patricia Marquis, Royal College of Nursing director for England, said: “Health and care is under huge strain in the run-up to Christmas. These figures suggest there is absolutely no slack in the system, which is dangerously close to overheating completely.
“A key part of the problem is that the vast majority of hospital beds are full – around 95% – including with thousands of patients fit to be discharged. The lack of community and social care means they’ll be spending this Christmas in hospital.
“The real cause of this is record nursing vacancies in the NHS and tens of thousands more across health and social care. Ministers can only begin to fix this by addressing the record nursing vacancies and valuing the profession properly by paying nurses fairly to retain and recruit the staff patients need.”
The Patient Association chief executive Rachel Power said the situation was "complex" and would be difficult to resolve quickly.
She told the BBC: "The crisis the NHS has been in for many months now stretches from people waiting for an ambulance, right through the system to people stuck in hospital unable to be discharged for lack of social care to support them once they are home.
"If hospitals cannot discharge the medically fit from hospital, A&E departments can't transfer patients that need a hospital bed on to a ward, and paramedics cannot hand over patients waiting in ambulance to A&E staff.
"For patients, the situation is frustrating and frightening."