Hospital emergency departments in Wales are "on the edge", with some patients waiting for more than 24 hours, according to a leading doctor.
There are problems with recruiting emergency medicine consultants and issues with bed blocking, Dr Robin Roop, of the Royal College of Emergency Medicine, warned.
Dr Roop, the head of the college in Wales, said A&E departments were at "critical levels" and the problem had persisted for a year rather than being a winter crisis.
"The health boards have learnt from previous years about winter pressures and what needs to be done - things like expanding bed capacity and changing elective operations - they've worked to a small degree," he told the BBC.
"But we still see a reduction in the number of patients being able to be passed on (from emergency units) in a timely fashion. And we still see exit-blocks.
"It means staff aren't doing what they've been trained to do in emergency medicine. They are now doing the additional things of looking after for longer because of the delays.
"There are patients waiting over four hours a lot of the time. So those patients have to be treated as a ward-based type of patient. The statistics show some patients spend over 12 hours in the department and some over 24 hours."
Dr Roop, a consultant in Wrexham, warned that winter pressures including flu cases could add to the problem: "Absolutely every emergency department (in Wales) is on the edge - we are ever so close to patients becoming really poorly in our departments and that could have a knock-on effect and having disastrous outcomes."
He told the BBC Radio 4 Today programme: "Emergency departments should be able to deal with the workload that they have but the problem lies with the exit blocking within the emergency departments - that's patients who are unable to move out of emergency departments on to their designated wards at the appropriate time."
Part of that was due to the "delayed transfer" of care, he said.
"Patients are unable to get out of the hospital in a timely fashion either to a community setting or back to their homes because of the inability to get social care set up for them."
A Welsh Government spokesman told the BBC: "There was a 23% reduction in the number of people who spent more than 12 hours in emergency departments in December compared to November but we know there is more work to do.
"We expect all health boards to ensure they have the right mix of staff to ensure services are safe, sustainable, and to ensure patient experience and outcomes are optimised."
The chief executive of NHS Wales acknowledged there was a need to recruit more consultants and said efforts were being made to ease problems of bed blocking.
Dr Andrew Goodhall told Today: "The winter will always be a more exceptional period of time, but I agree with Robin - this is a year-round pressure we experience in Wales.
"Certainly in terms of his call for needing to move to recruit additional consultants, I agree with that - Robin and I have spoken about this many times - and over the last five years we have recruited an extra 50% of consultants in A&E departments across Wales and we continue to need to do more."
Pressed on why patients had to wait in A&E for more than 24 hours, he said: "It is important that patients are cared for safely; it is why we need to look at some of the reasons for the demand coming into the system."
He added: "We know that there are patients coming into our A&E departments that could have accessed alternative services."
Dr Goodhall said efforts were being made to ease the pressure on the system: "Increasingly we need to make sure that we focus on some of the blocks in hospitals so, for example, delayed transfers of care - we put additional money into our intermediate care fund in Wales and we have seen progress with recent improvements in the delayed transfers of care in the system in Wales as we target those broader issues."