The Welsh Ambulance Service has declared a critical incident because of increased demand across the 999 service and extensive hospital handover delays.
It said more than 340 calls were waiting to be answered across Wales at the time the critical incident was declared on Monday evening.
In addition, more than half of the trust’s ambulance vehicles were waiting to handover patients outside hospitals.
The service is urging the public to call 999 only for serious emergencies as some patients continue to wait many hours for an ambulance.
The trust said it has taken additional measures to ensure it can continue to deliver a service to the public.
Head of service at the trust, Stephen Sheldon, said the public can help by only calling 999 in the event of a life-threatening emergency.
“That’s a cardiac arrest, chest pain or breathing difficulties, loss of consciousness, choking, or catastrophic bleeding,” Mr Sheldon added.
The service is advising the public to visit the NHS 111 Wales website for health advice or to consult a GP, pharmacist, or minor injuries unit.
The Welsh Ambulance Service described the situation as “very rare”.
A critical incident was also declared in December 2020, due to high demand, particularly in south east Wales.
But an extraordinary incident was declared in 2023 after an ambulance spent more than 28 hours outside a hospital.
The Welsh Ambulance Service said 16 ambulances had waited outside the emergency department at Morriston Hospital, Swansea, at one time, having a knock-on effect on other services.
Following this, then First Minister Mark Drakeford said declaring such an incident was a tool used by those running the service to allow for “mutual aid” to be brought in.
He also warned more were likely to be called.
Monday’s critical incident declaration came after several health boards implemented new rules for patients and visitors to control the spread of infection amid concerns about an increase in flu cases.
Cardiff and Vale, Hywel Dda, Aneurin Bevan and Cwm Taf Morgannwg health boards all introduced face coverings rules over the weekend.
On Monday, Swansea Bay and Betsi Cadwaladr said that people must try and temporarily avoid hospital visits, and staff and visitors must wear face masks at all times, to help minimise the spread of flu.
