Ambulance bosses have pleaded with people to call 999 only in “life-threatening emergencies” after many patients were left waiting outside hospitals in freezing conditions.
Emergency teams in north-west England said 100 ambulances were being held outside hospitals on Monday night as a result of delays in handing over patients.
At the same time, a further 600 people, many potentially seriously ill, were waiting for ambulances across the region, which includes Greater Manchester, Liverpool, Lancashire and Cumbria.
NHS leaders said the sub-zero temperatures were adding to the huge strain on emergency services across Britain.
It comes as up to 100,000 nurses prepare to go on strike across England, Wales and Northern Ireland on Thursday in the first widespread industrial action of its kind.
Paramedics and other ambulance workers are then due to strike across large parts of England and Wales next Wednesday.
North West ambulance service, one of those due to be affected by strike action next week, issued what it called an “urgent appeal” to the public after long delays outside hospitals on Monday night.
It said “a combination of factors, including severe weather and hospital handover delays” was slowing its response times and that people should only call 999 in “life-threatening emergencies”.
These include cardiac arrest, severe bleeding, serious head injuries and suspected stroke.
Ged Blezard, director of operations at North West ambulance service, said: “Please only call 999 if someone has a serious illness or injury, you think their life is at risk, and you cannot get them to hospital by any other means.
“We know there are patients waiting for our help and we are sorry that we are unable to respond as quickly as we would like. Please be assured that we will get to you as soon as we can.
“The public can help us by only calling 999 for life-threatening emergencies. We cannot stress enough that our ambulance crews are reserved for the most life-threatening cases and these incidents will be prioritised.
“Please do not call 999 to check on ambulance arrival times, we cannot answer this question, and this blocks the line for other calls trying to get through.
“For all other health concerns, it is likely we will direct you to alternative services, so please help us by first checking your symptoms at 111.nhs.uk and call on friends or relatives for transport if necessary.”