Hospitals in England could be on the brink of collapse, leading doctors say.
The Royal College of Physicians said the triple effect of rising demand, increasingly complex cases and falling bed numbers was causing problems.
The college's report claimed urgent care was already being compromised and warned the situation would get worse unless something was done.
But the government rejected the suggestion, saying the NHS was ready for the challenges it was facing.
The college said in some ways the NHS had been a victim of its own success.
Advances in medicine had led to people living longer, but this meant they were increasingly developing complex long-term conditions such as dementia as a result.
It said this had been happening during a period of falling bed numbers - they have been reduced by a third in the past 25 years - and rising numbers of emergency admissions.
The RCP said standards were slipping in hospitals throughout England.
It cited the way older patients were repeatedly moved around wards, the lack of continuity of care while in hospital and tests being done during the night as some of the examples of how care was suffering.
The college also highlighted the results of feedback from its members, which showed concern about discharge arrangements and workload.
And it warned the problems could lead to another scandal like that surrounding the Mid Staffordshire NHS Trust, which became the subject of a public inquiry after regulators said poor standards had led to needless deaths.
Prof Tim Evans, of the RCP, said: "This evidence is very distressing. All hospital patients deserve to receive safe, high-quality sustainable care centred around their needs.
"Yet it is increasingly clear that our hospitals are struggling to cope with the challenge of an ageing population who increasingly present to our hospitals with multiple, complex diseases.
"We must act now to make the drastic changes required to provide the care they deserve."
The report said the solution lay in concentrating hospital services in fewer, larger sites that were able to provide excellent care round-the-clock, seven days a week.
But it also said this would require improvements in community services as there were many patients who ended up in hospital because of a lack of help close to home.
Jeremy Hughes, chief executive of the Alzheimer's Society, said: "These latest findings are alarming but, unfortunately, not surprising.
"It is painfully evident that the healthcare system stands on the brink of crisis.
"People with dementia are going into hospital unnecessarily, staying in too long and coming out worse."
Health minister Dr Dan Poulter said: "It is completely wrong to suggest that the NHS cannot cope - the NHS only uses approximately 85% of the beds it has available, and more and more patients are being treated out of hospital, in the community or at home.
"But it is true that the NHS needs fundamental reform to cope with the challenges of the future.
"To truly provide dignity in care for older people, we need to see even more care out of hospitals. That's why we are modernising the NHS and putting the people who best understand patient's needs, doctors and nurses, in charge."