The NHS will struggle to cope if the Government fails to tackle the social care crisis, the British Medical Association has warned.
Health and social care services are "desperately trying to prop up" one another but are "cracking under the weight", BMA chairman Dr Mark Porter said in his new year message.
The stark warning comes as analysis by the doctors' trade union revealed controversial plans will need to deliver £26 billion of cuts from health and social care costs by 2020-21 to balance spending.
Health managers in 44 areas of England have been ordered to draw up strategies, setting out how they will reduce costs, change services and reduce care after a record £2.45 billion deficit for the past financial year.
The sustainability and transformation plans (STPs), some of which have been published or leaked, could see some hospitals, accident and emergency units or maternity centres close and other services merge.
Dr Porter said STPs had revealed the health service was "unsustainable" without "urgent further investment", adding: "STPs will only succeed if they are realistic, properly funded and have patient care as their priority."
The BMA said in November that £22 billion of cuts would need to be delivered by STPs, but this figure has risen following analysis of saving figures found in documents from all 44 areas.
Cuts to social care amount to £5 billion of the overall £26 billion that needs to be saved - though in some areas the reductions are almost as great as those to healthcare, the BMA said.
Dr Porter said the care crisis was having a knock-on-effect on the NHS, with a lack of social care for patients causing bed shortages.
"STPs are meant to bring health and social care together, and in a grim kind of way they do," Dr Porter said.
"It is clear from many STPs that each is desperately trying to prop up the other, their crutches cracking under the weight.
"When social care is on its knees, patients suffer delayed transfers and the personal and financial cost is vast."
Barbara Keeley, Labour's shadow minister for older people, social care and carers, said planned cuts to services are "worse than feared" in some areas.
She said: "What these cuts will mean is more older and vulnerable people having to manage without the care they need. They will also mean even more people stuck in hospital because they are waiting for care services.
"It is time for Jeremy Hunt and Philip Hammond to listen to health professionals and face up to the crisis in social care that they have created, reverse plans for further damaging cuts and fund social care as the public expect and older people need."
Liberal Democrat health spokesman Norman Lamb added: "This Government's chronic neglect of social care is a national disgrace.
"Conservative ministers may not have to take out crippling loans to pay for the care of a loved one, but millions of other people do. We must be honest about the scale of this crisis and bold about the solutions.
"If ensuring older people are treated with the dignity they deserve means paying a little more in tax, we should be prepared to say it."
A Department of Health spokeswoman said: "As well as several billion more for the NHS, we have announced almost £900 million of additional funding over the next two years for social care to tackle the growing pressures of an ageing population, but we know that money alone is not the solution.
"Many councils are already providing high-quality social care services within existing budgets.
"Sustainability and transformation plans will provide a health and care system ready for the future, ensuring the best standards of care, with local hospitals and councils working together in conjunction with local communities for the first time."