Waiting time targets in England are being missed as hospitals struggle to cope with a record number of admissions.
Figures released by NHS England show just 89.8% of patients were seen within four hours last week, compared to the target of 95%.
More than 10,000 patients were forced to wait longer than four hours for a bed once a decision was made to admit them into hospital from A&E.
The figure for the same period last year was fewer than 4,000.
There were 111,062 emergency admissions last week, which was the highest number since records began over a decade ago.
Dr Mark Porter, British Medical Association chairman, said: " These figures confirm just how much pressure the NHS is under.
"Staff are working flat out but the system is really struggling to cope with the sheer number of patients coming through the door.
"Growing pressure on services throughout the year means hospitals have no spare capacity to deal with the winter spike in demand. So patients are enduring delays in their treatment, and the NHS finds itself running just to stand still."
Some 440,428 patients attended A&E last week, which was over 24,000 more than during the same period last year.
Dr Barbara Hakin, national director of commissioning operations for NHS England, said: "Pressures on our A&E services continue to increase significantly.
"We have admitted more people to hospital this week (ending December 14) to take care of them than in any previous week on record. I want to pay tribute to the staff dealing with that - they are doing a brilliant job.
"While we are now below the extremely high waiting time standards that we set ourselves, the service we provide remains robust."
The failure to hit waiting time targets was blamed on "misguided cuts" and "complacency".
Dr Peter Carter, chief executive of the Royal College of Nursing, said: " Although patient numbers are rising, NHS trusts can't hire enough nurses because of misguided cuts to training places.
"There are too few beds available for all the patients coming into A&E and under-resourced community services and cutbacks to social care provision also mean that many patients aren't able to be discharged from hospital."
Shadow health secretary Andy Burnham claimed David Cameron had allowed the NHS to "sink into crisis".
He said: " Labour has been warning the Government all year about the growing crisis in A&E, but it failed to bring forward a credible plan to halt this decline.
"It is now a serious situation and the Government's complacency is becoming dangerous. It proves they can't be trusted with the NHS."
Richard Hawkes, chairman of the Care and Support Alliance - which represents more than 75 of Britain's leading charities, said: "The pressure on our health system is being intensified by the squeeze on council-funded local care.
"Chronic underfunding has left hundreds of thousands of older and disabled people, who need support to do the basics like getting up or out of the house, cut out of the care system
"The impact is now being felt throughout the health and care system and the health service is forced to pick up the pieces when people become isolated, can't live on their own and slip into crisis."
A Department of Health spokesman said: " We know the NHS is busier than ever before, which is why we've given the NHS a record £700 million this winter for more doctors, nurses and beds. The NHS has ensured there are plans in every area to manage the extra demand."
Richard Murray, director of policy at The King's Fund, an independent charity working to improve health and health care in England, said it is very likely the reason why the waiting times in A&E are lengthening so quickly is because there are a lot of people sitting in A&E waiting for a bed.
"Hospitals don't have the staff or the beds to admit them, so the two are very much linked," he said.
Mr Murray said that while the number of admissions are at their highest ever, they have been rising throughout the year.
He said that while they have continued to rise into winter and that is not unusual, the speed at which they have been going up is "very unusual, particularly given that the weather isn't particularly bad, there isn't yet sign of a flu/virus moving through the population".
He added: "The usual culprits that drive people into A&E and make hospitals admit them don't really seem to be at play."
Mr Murray said the number of admissions is rising much faster than the rate of the population increasing.
"If you look at the number of people that were admitted as an emergency through A&E alone, it's up by just under 6% over the last year. Well, the population of England has not risen by just under 6% in one year.
"And a lot of the rise in population in England, many people point to migrants and young people coming from abroad ... they don't get that sick. These are not the people that are in A&E needing a hospital bed," he said.
Mr Murray said primarily the people needing hospital beds are people who are "very sick", and in many cases are elderly or have other illnesses.
He said an increase in staff by the NHS over the last two years, particularly nursing staff, has not kept pace with the increasing numbers of people that need admitting.
Mr Murray pointed out that while England may have an ageing population, people "only get older one day at a time", adding: "There needs to be something else behind this. The pressure from a rising population and an ageing population push up the numbers going into the NHS, but not as quickly as we've seen."
He said a number of people are beginning to point to the fact that social care budgets and social services budgets have been hit, or that sometimes people find it difficult to see a GP meaning that they may get more ill.
"People seem to have got sicker outside of hospital and then need the hospital to look after them, and I think that's why a lot of people now are looking at the other factors, about what community services look like, what GP services look like and what's happened to social care, where local authorities, with their budgets being cut, have been forced to pull back the amount of care they provide to people in their own homes," he said.
Mr Murray said it will be "quite hard to do anything about this quickly", adding: "I fear slightly we are at the mercy of the plans that the NHS has already laid."
He said there needs to be a fundamental look at what has provoked this increase in the number of people needing hospital care, because if it keeps on going up, you can not just keep recruiting tens of thousands more nurses.
"The numbers are rising so quickly, we need to work out quite fast what it is that's making people ill enough to mean that they need a bed in hospital, and how to get them through very quickly, and that's likely to mean something in community services, in GP services.
"So again, once you have been admitted, the hospital and the consultants in the hospital, are confident enough to discharge you as soon as they can, so they can free the bed and bring somebody else in," he said.
Caroline Abrahams, charity director of Age UK, said: "The fact that A&E has just had its busiest week ever is frightening news. In most years demand on A&E peaks after Christmas, so it makes you wonder how hospitals will cope in January and February.
"One of the greatest problems hospitals face is discharging older people home safely, so they can get back on their feet again. From this point of view social care is a crucial 'pressure valve' for the NHS.
"And it's the inability of councils to meet the demand for social care that means thousands of older people are ending up staying in hospital longer than their medical condition warrants, intensifying the pressure on hospital beds.
"The truth is there will be no long term solution to the NHS winter crises until Government investment in social care - in the form of its central grant to councils - significantly rises. As it is, experts say that the local government funding settlement that has just been announced amounts to a real terms cut. Age UK's biggest worry is that many older people will suffer the consequences."