More than four in 10 hospitals in England declared a major alert in the first week of this year, new figures have shown.
As A&E departments are overwhelmed and the health service comes under increasing pressure, the data from NHS England shows the crisis is growing - and NHS bosses warn the flu peak has not yet hit.
Overall, NHS hospitals issued 222 serious alerts in six days.
The NHS England data, which covers the period up to January 8, shows the overall number of alerts was around six times higher in the six days up to last Sunday, compared to the previous six days (from December 28 to January 2).
Six NHS trusts reported a "level 4" alert, meaning patient safety was at risk, at least once during the week.
Those six trusts were:
University Hospitals Bristol NHS Foundation Trust
North Bristol NHS Trust
Royal Liverpool and Broadgreen University Hospitals NHS Trust
University Hospitals of Leicester NHS Trust
University Hospitals of North Midlands NHS Trust
Southport and Ormskirk Hospital NHS Trust
In total, 25 trusts declared major alerts every day between January 3 and January 8.
The number of major alerts - previously called red and black alerts - is the highest of the winter.
The figures come as trusts confirmed they have cancelled operations and procedures to ease pressure.
The John Radcliffe in Oxford confirmed it had cancelled all non-urgent planned operations and admissions on Friday and Monday.
Around 20 procedures have been cancelled at Northern Lincolnshire and Goole NHS Foundation Trust while planned procedures have also been postponed at Leicester's Hospitals, although the trust declined to say how many.
At a Downing Street media conference, Prime Minister Theresa May acknowledged the NHS as under pressure.
"We always see increased pressures in the NHS over the winter period. That's why in preparing for the winter period this time, £400 million was put in to ensure that winter-preparedness," she said.