The number of A&E visits in England soared by more than 400,000 in 2014, figures show.
The College of Emergency Medicine said that was the equivalent of filling an extra nine emergency departments.
The Health Select Committee has been taking evidence after the worst waiting times in A&E for a decade and many hospitals declaring "major incidents".
Doctors said it was "absurd" to blame patients, who were advised to go to A&E by services including NHS 111.
The committee heard the reasons for the surge in demand were "many, varied and complex", but staff were doing a "heroic" job.Continue reading the main story
Figures for England showed 92.6% of patients had been seen within four hours during the October-to-December quarter. The target is 95%.
Then, last week, data for the start of the new year showed the proportion had dropped to a new weekly low of 86.7%.
The figures include walk-in centres and minor injury units. Once you strip them out, just one in seven major A&E units are hitting the target.More people
Data from NHS England shows there were over 14.6m visits to A&E in 2014 - an increase of 446,049 on 2013.
Dr Clifford Mann, the president of the College of Emergency Medicine, told the committee: "Now the interesting thing about that is many people would describe that as only a 3% increase in attendances.
"That's certainly true, but the other way of describing it is to say that's equivalent to eight or nine extra emergency departments and of course we haven't built or staffed eight or nine extra emergency departments in the last 12 months."
Other parts of the UK are also missing the four-hour target with waits in Northern Ireland and Wales even worse than in England.
The four-hour target measures the point from when the patient arrives to when they are treated and discharged, admitted to hospital or transferred to another part of the NHS.
Prof Chris Ham, from The King's Fund health think tank, said there was no simple explanation for the extra pressures on A&E.
He said: "The causes are many, varied and complex. We think the most important causes are outside hospital."
He cited under-investment in GP services and a lack of community services to support people being discharged from hospital.'Don't blame patients'
Dr Mann said it was not the fault of patients, who were often told to go to A&E, including through the helpline service, NHS 111.
He said: "I don't think you should blame people for attending an emergency department when we've told them to go there, it's absurd."
The pressures being felt in A&E are also affecting other parts of the hospital system.AnalysisBy Hugh Pym, BBC Health Editor
The Government has made much of the £700m of extra funding made available to the NHS in England to cope with winter pressures. But has it all reached the frontline?
Doubt was cast on that by Dr Cliff Mann of the College of Emergency Medicine. He told MPs that investment of the money was "geographically patchy".
Chris Ham of the King's Fund ventured that some of the money might be "papering over the cracks" of trusts struggling with deficits.
Dale Bywater of the Trust Development Authority argued that the money had been pledged early and was being closely tracked through the system.
Just how the extra cash for the NHS has been used will continue to be an issue as the debate over the intense pressures on A&E continues.
Delays are also being seen when ambulances hand over patients and inside the hospital when patients need to be found beds and when they are ready to be discharged.
The problems have even led to a number of hospitals declaring major incidents, which means they take steps such as calling in extra staff and cancelling routine operations, such as knee and hip operations.
The committee heard that pressures on A&E would have a knock-on effect on the rest of the health service as priorities shifted to target the four-hour wait.
Prof Ham warned other targets were likely to slip later in the year.
Prof Keith Willett, the director of acute care for NHS England, said: "We have to do a transformation of the whole system with a particular focus on out-of-hospital services being the way to both reduce demand and also alleviate the issues of congestion within the hospital.
"It isn't going to be a quick fix. We have said it will be three to five years to get all of these things in place."