A critical incident has been declared by South East Ambulance Service (SECAmb) on the eve of a strike by paramedics in a row over pay and conditions.
Officials said the decision, taken on Monday evening, followed a period of more than a week of “sustained pressure” across 999 and 111 services.
This had “significantly impacted on our ability to respond to patients,” the service said.
“We would like to thank all our staff and volunteers for their hard work and commitment in recent days in what continue to be extremely challenging circumstances,” it added.
SECAmb urged members of the public to continue calling 999 in life-threatening emergencies, with priority given to the most seriously ill and injured patients.
Patients can also continue to seek help and advice from alternatives including NHS 111, online at 111.nhs.uk, their own GP or by speaking to a pharmacist.
SECAmb said that declaring a critical incident “provides us with additional oversight and enables us to explore options including mutual aid, while focusing all efforts on frontline patient care.”
The situation will be kept under “close review,” it added.
North East Ambulance Service and the East of England Ambulance Service also have also declared critical incidents.
The northeast service operates across Northumberland, Tyne and Wear, County Durham, Darlington and Teesside.
The southeast covers Brighton & Hove, East Sussex, West Sussex, Kent, Surrey and North East Hampshire.
Eastern England covers Bedfordshire, Hertfordshire, Essex, Norfolk, Suffolk and Cambridgeshire.
North East Ambulance Service said it declared a critical incident on Monday afternoon as a result of "significant delays for more than 200 patients waiting for an ambulance, together with a reduction in ambulance crew availability to respond because of delays in handing over patients at the region’s hospitals".
Stephen Segasby, chief operating officer at the service, said: "Our service is under unprecedented pressure.
"Declaring a critical incident means we can focus our resources on those patients most in need and communicates the pressures we are under to our health system partners who can provide support.
"We are asking the public to call us only in a life-threatening emergency."
The East of England Ambulance Service, declaring critical incident status in a statement on Monday, said it was "currently under huge pressure as a consequence of 999 call volumes and hospital handover delays".
"Declaring a critical incident means we can ensure our resources are focused on patients with the greatest need, as well as allow us to access wider support from our health and care partners," the trust said.
The moves to declare critical incidents come as fears grow over the impact of an ambulance strike on Wednesday, when thousands of paramedics, technicians, control room workers and other staff walk out.
Health minister Will Quince has warned the public to avoid any “risky activities” on Wednesday as ambulance drivers take industrial action.
During the strike, the military will not drive ambulances on blue lights for the most serious calls but are expected to provide support on other calls.
The junior minister said that armed forces personnel would play a key role but would not be able to “break the law” when covering for ambulance workers.
Mr Quince urged the public to avoid anything risky on Wednesday, telling BBCBreakfast: “Where people are planning any risky activity, I would strongly encourage them not to do so because there will be disruption on the day.”
