A&E departments are buckling under the pressure of a social care system that is reaching its "tipping point", a health watchdog has warned.
Some people across the country are receiving "very poor care", the Care Quality Commission (CQC) said as it released its annual assessment of care in England.
Overall, three in five hospital trusts have been told they need to make improvements - with particular problems being highlighted in medical services and accident and emergency departments.
And 81% of acute NHS trusts are rated as either inadequate or requiring improvement in terms of safety.
The CQC has also set out a bleak picture of the social care sector across the country, which it says is linked to wider problems in the NHS.
"We have found too much acute care that we rated inadequate - particularly urgent and emergency services and medical services," the report stated.
The quality of care people received from health and care services in England varied considerably, the report added.
The report said that hospitals were under increasing pressure.
Just one in five NHS acute trusts were rated as "good" in terms of safety. None received the top rating of outstanding, the report showed.
Serious safety issues could include surgeons operating on a wrong body part or patients receiving the wrong medication.
The document also painted a woeful picture of social care.
"There are indications that the sustainability of adult social care is approaching a tipping point," it stated.
The watchdog said that despite a 33% rise in the number of people aged 85 and over in the last decade, the proportion of people receiving local authority-funded care had reduced.
It said the number of beds in nursing homes was not increasing in line with demand and care home providers were pulling out of local authority contracts as funding did not cover the costs of care.
The CQC called for "urgent action" to tackle the issues, including an injection of funding into the care system.
CQC chief executive David Behan said: "What's happening, we think, is that where people aren't getting access to care, and we are not preventing people's needs developing through adult social care, is that they are presenting at A&E.
"Emergency admissions of older people are increasing and we also know that the number of delayed bed days in hospital are increasing."
He added: "We think more resources need to be made available to adult social care. That will help people in adult social care and it will also improve the impact it is having on the system.
"Without urgent action being taken, we are concerned that there will be more people whose needs aren't being met, that improvement in adult social care will be harder to make and there is a risk that more services will deteriorate."
CQC said that most people received high quality and compassionate care but it questioned how long this could last given the pressures on the system.
A Department of Health spokeswoman said: "This report from our independent inspectorate shows that the majority of the NHS, 72% of adult social care services and 87% of GP practices inspected are good or better - and that improvement is taking place all over the country.
"The NHS is performing well at a time of increasing demand - the Government is investing £10 billion to fund its own plan for the future, and crucially is ensuring that the amount of money available to local authorities for social care is rising in future years of the Parliament, reaching up to £3.5 billion extra by 2020."
Margaret Willcox, vice-president of the Association of Directors of Adult Social Services, said: "We are at a tipping point where social care is in jeopardy and unless the Government addresses the underfunding of the sector, there will be worrying consequences for the care market, the NHS and, most importantly, for older and disabled people, their families and carers."
Izzi Seccombe, chairwoman of the Local Government Association's community wellbeing board, added: "Properly funding social care is essential if we are to move away from just trying to meet people's basic needs to ensuring they and their carers can live independent, fulfilling lives in safety and in control of their care, as well as alleviating the pressure on the NHS."
Caroline Abrahams, charity director at Age UK, said: "When any regulator says that it is worried that a service may be reaching a tipping point ?in terms of quality and sustainability, it is clearly time for very serious concern.
"Next month's Autumn Statement is an opportunity for the Government to give social care the priority it deserves in terms of public spending and this report shows how important it is that the Government acts.
"Otherwise 'a tipping point' threatens to become something infinitely worse, placing many older people at risk of harm."
Labour's shadow minister for mental health and social care, Barbara Keeley, said: "This report should set alarm bells ringing right across government about the very real crisis facing health and care services in England today.
"Unless Theresa May gets a grip of this situation there is a very real prospect of the care system deteriorating further and thousands of people being left without the support they need to live well at home."
Katherine Murphy, chief executive of The Patients Association, said the report was "sobering", adding: "Whilst there are nuggets of positive examples of Trusts successfully swimming against the tide, fundamentally, the tide has turned and the pressures are becoming so great that the health and social care sector is struggling to meet demand whilst delivering excellent quality care."
An NHS England spokesperson, said: "This report confirms exactly what the Forward View said, that the NHS will not be able to care properly for the growing population of frail older people unless the availability of social care increases in line with rising need.
"Turning to primary care, since GPs provide the vast majority of NHS services - over 300 million patient visits a year - it is particularly pleasing that the CQC report they are the provider sector providing the highest proportion of good and outstanding care.
"They also highlight that collaborative local leadership goes hand in hand with good care, one reason why we asked all parts of the health and social care system to agree plans for transforming services, engaging widely with the public and patients in doing so."