South Western Ambulance Service (SWAS) has declared a critical incident and issued an urgent appeal to the public.
The service is asking people to think carefully before dialling 999, after 473 patients in the region were left waiting for ambulances by midday yesterday and 123 ambulances were at a standstill, waiting to hand over patients outside hospitals.
The service said a combination of the cold weather, busy hospitals and strike action are all contributing to the challenges it is facing.
Members of the GMB and Unison unions are striking later today in a dispute over pay and staffing levels.
Health secretary Steve Barclay said workers’ pay demands are "unaffordable" but that funding the NHS is a priority.
Ahead of the strikes, Will Warrender, chief executive at the South Western Ambulance Service, said: “Please help us to help those patients who need us most by only calling 999 if a patient has a life-threatening condition or illness.
“We know there are patients waiting for an ambulance, and we will get to you as soon as we can. We are sorry that we are unable to respond as quickly as we would like.
“We are doing all we can to manage winter pressures and the upcoming industrial action, including receiving military support during industrial action days which will allow our ambulance clinicians to be manning more ambulances and reach patients more quickly.”
He added: “The public can help us by only calling 999 for life-threatening emergencies, we absolutely must have crews available for the most life-threatening conditions and we will be prioritising these patients.
“Please do not call back asking for an estimated time of arrival of an ambulance. We cannot provide this information and it blocks our lines from other callers reaching us.
“If the condition of a patient is not life-threatening, we may direct you to alternative services. So please help us by accessing the right service for the care you need.
“I’d like to express my huge thanks to our people and NHS partners working to deliver the best possible care they can for our patients over the coming weeks.”
The service has urged that people call 111 for advice and support.
It says 999 should only be called for life-threatening emergencies such as cardiac arrest, loss of consciousness, fits that aren’t stopping, chest pain, breathing difficulties, severe bleeding, severe allergic reactions, suspected stroke and serious head injuries.