Patients are significantly more likely to be admitted to hospital in the 10 minutes before a key target could be breached than at any other time, figures show.
Some 59% of patients are admitted to hospital in the final 10 minutes of a four-hour wait at A&E compared to just 10% of patients who spend 10 minutes in A&E.
The report, which covers England, was published by the Health and Social Care Information Centre (HSCIC) and shows that the longer people spend in A&E the more likely they are to be admitted.
A fifth (20%) of patients who spend between two hours, 41 minutes and two hours, 50 minutes in A&E are admitted, rising to 39% of those who spend between three hours, 31 minutes and three hours, 40 minutes there.
The Government's target says patients must be admitted or discharged within four hours.
A National Audit Office (NAO) report in October said the four-hour target was one of the main drivers behind an increase in the number of patients admitted to hospital who only stayed a short time.
It said the target "is likely to be one of the main reasons for the increase in short-stay emergency admissions".
Today's report also showed that almost one in two patients (47%) over the age of 64 are now admitted to hospital compared to around one in five patients of all ages.
During winter months, emergency admissions among older people and children under 10 are higher than for other age groups.
Since 2009/10, around a third of patients are also discharged from A&E after being given guidance or advice only.
The report also showed that most people attend A&E during the working hours of 9am to 6pm rather than overnight.
The study said the "pattern of arrival time by hour of day has remained consistent over the past five years".
Furthermore, the number of attendances at major A&E units (known as type 1) have risen only slightly above the rate of population increase.
This compares to attendances at minor units, which have risen at 11 times the rate of population increase over the time period 2004/05 to 2012/13.
Kingsley Manning, chair of the HSCIC, said there had been a "subtle shift" in the mix of people seen at A&E, towards more elderly people being seen.
"It's a subtle shift, it's not dramatic," he said.
Of the patients who end up discharged from A&E with guidance or advice only, he said a very small number of people turn up at A&E departments willingly.
"We assume a large proportion of them felt they needed to go there."
Asked about whether changes to GP contracts in 2004 - which enabled GPs to opt out of providing out-of-hours care - had had an impact, he said there was "no obvious relationship" in the data between attendances and changes in primary care provision.
Labour said the Government had been arguing that changes to the GP contract in 2004 had led to overwhelming numbers of people attending A&E, whereas the data showed attendances at major units had barely changed.
Shadow health secretary Andy Burnham said: "These embarrassing figures expose a year of spin and excuses on A&E from (Prime Minister) David Cameron and (Health Secretary) Jeremy Hunt.
"They prove that A&E has got steadily worse on their watch and blow apart repeated attempts to evade responsibility for the current crisis.
"They have diverted attention from the real causes of the pressure and allowed this crisis to deteriorate, putting spin before patient safety in an appalling abdication of responsibility.
"David Cameron broke his promise of 'no top-down re-organisation' - and threw the NHS into chaos.
"Under him, it has got harder to get a GP appointment after he scrapped Labour's guarantee of an appointment within 48 hours.
"Add to that deep cuts to social care support and the closure of a quarter of NHS walk-in centres, you have all the ingredients for the current A&E crisis."
Mark Porter, chairman of the British Medical Association (BMA), said: " Rising attendance rates, coupled with the Government's drive to do more with less, mean many emergency departments are under extreme pressure and are close to capacity.
"To alleviate pressure and reduce unnecessary attendance we need to ensure patients know how and where to access appropriate care and that they get the right advice first time round.
"Key to this is having an effective out-of-hours telephone service, yet the disastrous introduction of NHS 111 replaced a clinician-led service with a call centre and was responsible for many people being wrongly directed to emergency departments."
Dr Porter said elderly patients are often admitted to hospital "because of poor access to more appropriate community-based services".
Julia Manning, chief executive of the think-tank 2020 Health, said: "The fact that so many people are admitted in these last 10 minutes shows that doctors and nurses are watching the clock and not thinking about the best way to care for patients.
"We are really concerned that this is a very perverse target.
"It is also why so many people go to A&E in the first place who don't need to be there. They know they will be seen within four hours and they can't be bothered to sit on the phone or wait for a GP appointment.
"The target effectively tells them 'Come here, you will be seen within four hours'."
A health spokeswoman for the Conservatives said: "We know demand for A&E services is increasing as the population ages, with more people needing more healthcare.
"That's why we are tackling both the short and long-term problems: transforming out-of-hospital care by reversing Labour's disastrous changes to the 2004 GP contract, joining up the health and social care system, and backing health systems with £400 million to prepare for this winter.
"Winter is always tough but the NHS has never been more prepared, and in the face of unprecedented demand A&E performance is holding up well, with consultant numbers up and waiting times down under this Government."
Today's report shows there has been a small increase in the number of over-65s attending major A&E units.
As a proportion of overall attendances, they now account for 21% of the total - up from 19% four years ago.