Some Brits in urgent need of medical assistance will be forced to make their own way to A&E tomorrow.
NHS strikes mean people in affected regions have been warned they'll need to book taxis rather than expect an ambulance - while the Health minister's advice is not to do anything "risky".
In certain areas of the UK heart attack and stroke victims won't even be able to get an ambulance during the mass walkout, as underpaid and over-worked NHS staff down tools tomorrow.
It comes as tens of thousands of appointments and ops, as well as cancer care, are due to be hit today due to the second nurse strike.
National health bosses have warned eight in 10 ambulances could be delayed or not operating at all.
Union chiefs are threatening more disruption in the new year if ministers refuse to meet pay demands after more than a decade of crippling austerity.
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In the North West anyone who needs to get from their GP, critical care centre or care home to hospital are reportedly being told to rely on “self-conveyance or taxi conveyance”.
During what will be the first ambulance strikes in decades, only Category One calls are being guaranteed ambulances - around 15% of incidents.
Meanwhile health minister Will Quince said: “Where people are planning any risky activity, I would strongly encourage them not to do so.”
Health Secretary Steve Barclay told Brits to be braced for "severe impact" during the walkouts but has told those in need to still call 999.
A No10 spokesman said: “It’s only fair that patients are given clarity about what care patients will get on strike days.”
North East Ambulance Service declared a “critical incident” earlier this week because of “unprecedented pressure”.
The Times reports striking staff will only attend Category One and Two calls "in a public place".
Ben Holdaway, director of operations at East Midlands Ambulance Service, said: “Our responses to our patients will be much slower on the day.”
Chief operating officer Stephen Segasby said: “Declaring a critical incident means we can focus our resources on patients most in need.”
He added: “Ambulances will still be able to respond during the strike, but this will only be where there is an immediate risk to life.”
North West Ambulance Service said it would not collect patients from a GP surgery, care home or walk-in centre unless their heart or breathing stops.
More than 25,000 ambulance staff could strike on Wednesday, with a second day set for December 28.
Unions have assured emergency cover plans are in place.