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.