An ambulance spent 28 hours outside a hospital after an “extraordinary incident” was declared due to delays.
The Welsh Ambulance Service said 16 ambulances had waited outside the emergency department at Morriston Hospital, Swansea, at one time.
It said multiple sites across Wales were affected, “specifically” in the Swansea Bay health board area.
Lee Brooks, director of operations, told BBC Radio Wales Breakfast the situation was “heart-breaking”.
The service said people should only call 999 if their emergency was “life or limb threatening”.
Judith Bryce, assistant director of operations at the Welsh Ambulance Service, said on Sunday the service was experiencing “patient handover delays outside of emergency departments”.
“This is taking its toll on our ability to respond within the community,” she said.
“Approaching our declaration of an extraordinary incident, we have experienced multiple episodes of prolonged patient handover at multiple sites across Wales.”
She said additional managerial and clinical support had been brought in at Morriston.
“Regrettably, this means that some patients may be asked to make alternative hospital travel arrangements if an ambulance is not available,” she said.
“We apologise for the consequence of this action and ask the public to please use services wisely.”
On Monday, Mr Brooks said the situation had been “particularly challenging”.
“We had a couple of sites across Wales where we were experiencing long waits for patients to move from ambulances to emergency departments, but most of it at Morriston Hospital in Swansea,” he said.
“When that happens that of course has an impact on our ability to respond to other patients in the community.”
He added the trust was “creating more capacity to respond to patients” and that response to red category patients has “nearly doubled in the last three, four years”.
“Of course, by month we’re losing in the region of 19,000 hours, which is almost a week’s worth of ambulance capacity, so that’s quite a chunk taken out of our ability to respond.”
He said the problem was linked to “broader patient flow constraints” and was expected to worsen over the winter.
“This is generating a huge amount of frustration… it’s not a great experience for patients, it’s not great for dignity.”
He described the situation as “heart-breaking”.
Welsh Conservative health spokesman Russell George called the situation an “atrocious example” of the “wider Labour failure to run our Welsh NHS properly”.
He said that there needed to be “massive change in social care” and added that the Conservatives would “establish care hotels and encourage former NHS staff to become reservists to stop ambulances queuing outside of hospitals”.
The Welsh government has been approached for comment.
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