A&E doctors say pressure is threat to patient safety
Excessive pressure on A&E consultants has the potential to put patients at risk, doctors are warning.
The College of Emergency Medicine said increased demand and the complexity of work was causing staff sickness and burnout.
Its survey of just over 1,000 UK consultants found six in 10 thought their jobs were unsustainable.
It comes amid mounting concern about the ability of A&E units to cope this winter.
At the start of this year, the NHS in England missed its target of fewer than 5% of patients waiting more than four hours, as waiting times hit their highest rates for nine years.
Ministers have since announced a £500m bailout fund for the next two winters to help those hospitals with the most acute problems.
The college has always maintained that a shortage of doctors is a contributory factor to the problems.
Previous reports have highlighted the fact that A&Es do not have enough consultants.
The average is just over seven per unit when it should be 10 - and 16 for the largest hospitals - according to the college.
But now the college is warning that the shortages are beginning to affect the consultants who are in place.
In the survey, 94% complained they were working excessive hours - with more than half saying they were regularly doing more than a fifth extra on top of their contracted time.
The report also uncovered a small, but growing problem with consultants emigrating.
Last year 21 left the UK compared with three in 2008.
College vice president Dr Taj Hassan said: "Senior medical decision-makers in emergency medicine provide one of the most vital strands in maintaining safety.
"A failure to address these issues will compromise this ability and also further worsen the present workforce crisis."
Katherine Murphy, of the Patients Association, said the situation was "unacceptable".
"Patients have incredible respect for emergency medicine teams, but those teams need to be backed up with the funding they need to do their jobs without being stretched in this way."
A Department of Health spokesman commented: "We know we need to do more to support emergency departments to do their important work through winter and beyond.
"That is why we are investing £500m and we tasked Health Education England with developing plans to encourage more medical students to become A&E doctors in the future."
He also said a major review of the urgent and emergency care system - led by medical director Prof Sir Bruce Keogh - would be reporting shortly.