Around 2,000 ambulance hours have been lost over the past seven days due to delays at hospitals, ITV Wales understands.
It comes after ITV Wales also revealed that some hospitals in Wales have fallen more than 40% below one of their key A&E performance targets in recent days.
In a sign of the pressure being put on the Welsh NHS this winter, figures obtained by ITV Wales show that for the 24-hour period between the mornings of January 1, 2018 and January 2, 2018, Ysbyty Glan Clwyd ensured 48.8% of patients spent less than four hours in its A&E department. The target is 95%.
The target is for 95% of patients to spend less than four hours in an A&E department.
For the same time frame, ITV Wales understands Wrexham Maelor hospital managed 61% and Ysbyty Gwynedd managed 57.8% of patients spending less than four hours in A&E.
It means that Betsi Cadwaladr Health Board as whole had a figure of 55.7% for the 24-hour time frame.
Responding to the figures, the health board said the information was broadly accurate but that the data was not yet validated so was unable to provide further detail.
Betsi Cadwaladr's Director of Secondary Care, Nigel Lee said: "As has been seen across Wales, our Emergency Departments have been extremely busy throughout the New Year period. All of our staff are working extremely hard to provide care over the New Year period, and we thank them for their outstanding efforts over the last week.
"We are working closely with our partners at the Welsh Ambulance Service to ensure we meet the needs of patients most at risk, as well as with local authorities and colleagues in primary care.
“We urge patients to ensure they seek medical assistance from the service which best suits their needs. That way, they can receive care more quickly, and our emergency department staff can respond to people who need emergency care without delay.
Betsi Cadwaladr University Health Board is not the only health board to experience high demand for services over the Christmas and New Year period.
Cwm Taf University health board said its hospitals are running 'at level four'. This is the escalation level describing the pressure on the system as 'extreme'. It's the highest level.
Kath McGrath, acting chief operating officer for Cwm Taf University Health Board, said: “Cwm Taf UHB has implemented its winter plan which has supported us to manage demand over the Christmas and New Year period. The New Year period has been particularly busy, as anticipated at this time of year, and staff across the Health Board continue to work hard to deliver care to patients.
“Our A&E departments remain busy this morning and are currently at level four."
The same applied for the main hospitals within Aneurin Bevan University Health Board said.
A spokesman said: "Our hospitals remain under a great deal of pressure and we have opened extra bed capacity across the health board in accordance with our winter plans to help manage the recent increase in demand for services.
"During the Christmas and New Year period the Royal Gwent and Nevill Hall hospitals have been extremely busy due to an unusually high intake of very poorly people, particularly with clinically significant respiratory illnesses."
Cardiff and Vale health board said it too had been 'extremely busy' and that while it had opened some beds to meet demand, a small number of hospital beds have been closed to admission to avoid the spread of conditions such as flu.Our winter plan arrangements continue to be deployed and this has included opening additional ward beds at our UHW and UHL sites.
The Royal College of Emergency Medicine described the situation as 'dire' and 'horrific'.
Dr Robin Roop, head of the Royal College of Emergency Medicine in Wales said that Wales is not unique in the pressures facing its NHS but that there was 'no give' in the system.
"The system is not coping," he said. Dr Roop said that huge credit must go to staff who are working tirelessly to provide care but that the pressure is such that "people come to do a job and they can't do it."
Dr Roop added: “For staff, an Emergency Department feels like a battle field. We are fighting to safely treat an increasing number of acutely unwell patients, we are fighting to find enough staff to cover shifts 24/7 and we are fighting to find an available hospital bed for sick patients when there simply aren’t enough.
“The fact of the matter is that, despite the best efforts of all NHS staff, patient safety is being compromised daily. It is not acceptable that an increasing number of patients are being left on a trolley in a corridor, without satisfactory care. This is unsafe, undignified and distressing for patients and their family members.
“We are also seeing a high number of patients suffering from the flu this winter. This means that even more beds are made inaccessible to other unwell patients to, quite rightly, prevent the spread of this infectious disease."
A Welsh Government spokesperson said: “Winter and the period immediately after the new year bank holiday is always a challenging time for our health service, as it is across the UK, and we have been working with health boards and partners to ensure the NHS is prepared.
"This includes increasing capacity, for example by strengthening emergency ambulatory care services and increasing the number of beds available when demand is high.”
The increase in the volume of calls to the ambulance service compared to a normal day.
The Welsh Ambulance Service said it saw a 170% increase in calls over the first four hours of New Year's Day compared to a normal day. It said call handlers dealt with 721 calls between midnight and 4am, compared to the usual average of 267 calls in that time. On Boxing Day, the service said it received nearly 1,600 calls – 300 more than usual.
Richard Lee, the Welsh Ambulance Service's director of operations, said: “On New Year's Day, we received 1,000 calls more than expected.
“A large number of these calls were from people ringing us back to find out what time their ambulance would arrive.
“While we appreciate how anxious it can be to wait for assistance when you or your loved ones are ill or injured, we must stress that this ties up the phone lines for other patients.
“If we've arranged help for you, please only call us back if the patient's condition has deteriorated.