Cardiff and Vale University Health Board has tonight asked local people for support and to think twice before coming to the University Hospital of Wales' Emergency Unit.
It follows what they call an unprecedented influx of patients over the past 48 hours.
UHB Medical Director Dr. Graham Shortland said the health board was asking for support from the public to reduce the pressure on clinical teams, so they could focus on caring for the sickest patients.
While the sickest and most vulnerable patients are being seen promptly and there are no significant ambulance delays, we would like to ask local people to help us by not coming to hospital with minor illnesses or minor injuries that can be easily dealt with.
Patients who do come to the Emergency Unit with these minor conditions can expect significant waits for treatment, because we are mobilising our resources and focusing our energies on those patients with the greatest clinical need.
This is not a new message, and we ask people throughout the year to make sensible use of the Emergency Unit, but this is even more important when we have so many seriously ill patients at this time of year who need our care the most.”
The health minister Mark Drakeford has said the ambulance service must meet the challenges it faces. It comes after ITV News revealed last night that long lines of ambulances were waiting outside Wales' biggest hospital - The University hospital of Wales.
Concerns were raised last night after reports that queues of ambulances were waiting outside the University Hospital of Wales in Cardiff for hours to transfer patients.
A member of the public contacted ITV Cymru Wales claiming around 14 vehicles were outside A&E with patients inside.
Today Cardiff & The Vale University Health Board has denied that claim.
The board says at it's busiest point there were several ambulances outside and that was for less than an hour's wait.
A spokesman told ITV Cymru Wales 91 per cent of patients were seen within four hours and nobody waited for more than 12 hours.
The board says it is coping well during the busiest period of the year and it has not had to cancel any elective operations and wishes to reassure the public and thank staff for managing the demands on them.
Cardiff and Vale University Health Board says it has developed "a detailed action plan to make sure that we are addressing all areas" of concern, and the Royal College of Surgeons will visit again in September to see if there has been improvement.
The health board is looking at all options to increase cardiac surgery capacity, and looking at proposals to get patients treated more quickly.
Chief Executive Alun Cairns said the health board is working with surgeons "on a range of actions", and looking at what extra capacity could be provided, and improving how it manages emergency, care.
We know that we can do better and we have given priority to the issues raised in the RCS report.One of the main areas of concern has been the pressure on unscheduled care, seen here in Cardiff and the Vale, Wales and across the UK, and the impact that has on other services.
A great deal of engaging with clinical teams and partners such as the third sector and Local Authorities has been done over these issues and a number of pieces of work, directed and driven by clinical staff, are now starting to take effect.
– Adam Cairns, Chief Executive of Cardiff and Vale University Health Board
Wales' biggest hospital has been described as "dangerous", in a highly critical report from the Royal College of Surgeons.
It found that "patients are regularly dying on the waiting list from their cardiac pathology" and there was "universal consensus" among clinicians at the University Hospital of Wales in Cardiff that services there were "dangerous."
It warns "the current situation represents a severe risk to patients and urgent action is required."
"A wide range of concerns were raised" by clinical leads at the hospital during a routine visit by the RCS in April - the most prevalent was "the inability to admit patients for elective surgery." There were more than 2,000 operations either cancelled or not scheduled between January and March 2013.
"The main reason for this is the apparent unconstrained admission of emergency patients and the inability to effectively discharge patients", the report said.
Cardiff and Vale University Health Board is to carry out consultations with management and unions over staff reorganisation which could lead to redundancies.
The service change plans potentially affect around 385 employees says the health board.
“Many of these plans involve redesigning a number of services to deliver the same, or better, care in a different way, and in a more cost effective way. This includes reshaping the UHB’s workforce, in line with what has been proposed," says the board's Chief Executive, Adam Cairns.
The health board employs 14,500 staff and says redundancies will be a "last resort" and staff who need to change roles will be offered training to assume new responsibilities.