More than 10,000 ambulances a week are caught in queues of at least an hour outside accident-and-emergency units in England, a BBC News analysis shows.
The total – the highest since records began, in 2010 – means one in eight crews faced delays on this scale by mid-November.
Paramedics warned the problems were causing patients severe harm.
One family told BBC News an 85-year-old woman with a broken hip had waited 40 hours before a hospital admission.
She waited an “agonising” 14 hours for the ambulance to arrive and then 26 in the ambulance outside hospital.
When finally admitted, to the Royal Cornwall Hospital, which has apologised for her care, she had surgery.
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Ambulance system ‘facing perfect storm’
Both ambulance response times and A&E waits have hit their worst levels on record in all parts of the UK in recent months.
In Cornwall, patients facing emergencies such as heart attacks and strokes are now waiting more than two hours on average for an ambulance. The target is 18 minutes.
They are thought to be among the worst delays in the country but none of England’s ambulance services is close to the target, while Wales, Scotland and Northern Ireland are all missing their targets.
Alongside Cornwall, parts of Gloucestershire, Lincolnshire, Somerset and Bristol have the longest waits, Freedom of Information requests by the Liberal Democrats have revealed.
A key problem is the delays ambulances face handing over patients to A&E staff.
This is meant to happen within 15 minutes of arrival – but, as the BBC News analysis shows, regularly takes longer.
The College of Paramedics said crews were facing a “perfect storm”, with the queues outside A&E preventing them reaching patients who need a 999 response.
College chief executive Tracy Nicholls said: “We all know patients are coming to harm and in some cases severe harm.”
Government and local health chiefs’ attempts to tackle the problems were “not really making a dent” in the delays, she said, and the system was facing gridlock.
And even when patients are admitted into A&E, they can face long waits for a bed on a ward, with hospital bosses blaming a shortage of beds and problems discharging patients back into the community.