A hospital has temporarily cancelled all elective operations - even for cancer and urgent medical needs - after being overwhelmed with "exceptional levels" of patients who needed to be admitted.
Addenbrooke's in Cambridge is temporarily diverting ambulances to other hospitals and implored patients attending accident and emergency not to bring large numbers of people with them because "seating is at a premium".
The whole of Cambridge University Hospitals NHS Foundation Trust, which also runs the Rosie Hospital, is at the highest level of alert, known as Operational Pressures Escalation Level (Opel) 4.
A decision was taken on Tuesday morning to cancel all elective procedures apart from paediatric cases.
The trust has been on Opel 4 since Wednesday last week.
Reports suggest that at some points on Tuesday there were no free beds at Addenbrooke's, but it is understood that the Rosie Hospital's maternity care unit is operating as usual.
A Cambridge University Hospital spokesman said: "We can confirm that the hospital is at Opel Level Four, the highest level of alert, after seeing exceptional levels of acutely unwell patients needing inpatient beds.
"We are taking action to ease pressures and create flow through the hospital.
"We are temporarily diverting ambulances to other trusts and elective surgery has been cancelled. We would like to apologise to patients for the inconvenience.
"Patients can help us at this time by only coming into A&E if it is an accident or emergency and by not bringing large numbers of family or friends into the department where seating is at a premium.
"Details of further medical support can be found on the Cambridgeshire and Peterborough Clinical Commissioning Group website."
A 2016 NHS England document says Opel 4 is declared when "pressure in the local health and social care system continues to escalate leaving organisations unable to deliver comprehensive care. There is increased potential for patient care and safety to be compromised".
Hospitals in England were told to delay pre-planned operations and routine outpatient appointments for a month due to severe winter pressures throughout January.
But NHS England said cancer operations and time-critical procedures should go ahead as planned.