Delays in ambulances delivering patients to A&E departments in England have reached their highest level of the winter, new figures show, as hospitals struggle with mounting demands on their services.
A total of 16,900 people were forced to wait for more than 30 minutes to be seen by staff at emergency departments over the Christmas week, up from 11,900 the previous week, including 4,700 delayed for more than an hour.
NHS England's weekly operational update also showed non-emergency calls to the NHS hotline again reached a record high in the week ending December 31.
Calls to the health service's 111 service shot up 21% on the previous week to 480,400 - the most received in a single week since the hotline was created.
An NHS England spokesman said: "Hospitals, GPs, ambulances and other frontline NHS services have been extremely busy between Christmas and New Year, reporting higher levels of respiratory illness and some indications of increasing patient illness severity and flu.
"These increased pressures were mirrored in the NHS 111 service. In the week ending Sunday 31st December, NHS 111 responded to 480,000 calls, up 21% on the previous week.
"This is the highest number of weekly calls since the 111 service was created.
"In the light of these pressures, the medical and nursing-led National Emergency Pressures Panel has now enacted, for a time-limited period, the NHS' Winter Pressures Protocol to free up further staff and beds for patients needing urgent and emergency care."
The Department of Health says ambulance crews should be able to hand patients over to A&E staff within 15 minutes of arrival at hospital, and not doing so increases the risk to patients due to delays in diagnosis and treatment, as well as the chance that a patient will get worse while waiting on a trolley.
It comes as hospitals across the country compete with winter's annual spike in demand.
Tens of thousands of non-urgent operations and routine outpatient appointments have been shelved by NHS England to ease pressures on hospitals.
Bed occupancy rates climbed as high as 93.5% on New Year's Eve, up from 86.7% on Christmas Day, according to the data, with an average of 91.7% across the week.
In the previous week hospitals had reported bed occupancy levels of 90.9% - above the recommended safe limit of 85%.
Ambulances were forced to divert to different A&E departments on 39 occasions during Christmas week, down on 57 between Boxing Day and New Year's Day last year, figures show.
Public Health England (PHE) confirmed seven further flu-related deaths, taking the total so far this winter to 23.
There were 731 beds closed per day due to norovirus or diarrhoea and vomiting in Christmas week, below the average of 812, according to NHS England figures.
The figure for ambulance patients waiting more than an hour to be handed over to A&E staff during Christmas week nearly doubled on the week before.
In the days leading up to the festive break, 2,413 people were forced to wait more than 60 minutes to be seen in emergency departments.
Figures for ambulance delays of more than half an hour have gradually crept up since the start of the winter period.
Between November 20 and 26 there were 10,634 handover delays, rising to 14,323 in the week until December 17, before briefly dropping to 11,852 in the week ending on Christmas Eve.
New Year's Eve witnessed 12 hospital trusts report 100% bed occupancy, the biggest total for several weeks.
They included the Hillingdon Hospitals in London, Basildon and Thurrock University Hospitals, and the Queen Elizabeth Hospital in King's Lynn.
Growing strains on the NHS will see planned operations delayed for at least a month as staff sift through the most urgent cases.
Health Secretary Jeremy Hunt apologised to patients in England on Wednesday for the wave of cancellations, saying it was "absolutely not what I want".