Patients including pregnant women were put at risk by failings at one of the UK's largest NHS trusts, the chief inspector of hospitals said.
The maternity unit at Addenbrooke's Hospital was forced to close and divert patients elsewhere several times because of a shortage of midwives, according to Professor Sir Mike Richards of Care Quality Commission (CQC).
He spoke after it was revealed Cambridge University Hospitals NHS Foundation Trust (CUH), which runs the hospital in Cambridge, had been placed in special measures after inspectors deemed it "inadequate".
Prof Richards told BBC News that while hospital staff were "extremely caring and extremely skilled", senior management had "lost their grip on some of the basics".
He said: "They (patients) are being put at risk - it is not that we necessarily saw actual unsafe practice but we did see they would be put at risk if you don't, for example, have sufficient numbers of midwives for women in labour.
"That puts them at risk and it actually means that on several occasions the maternity unit has had to close and divert patients elsewhere."
The CQC's report, based on the inspection in April and May, found staff shortages and long-standing "serious" problems that had been ignored.
In maternity, inspectors raised "serious concerns", including a low midwife-to-birth ratio, and noted wards were closed regularly and equipment was old.
In one case example, high levels of nitrous oxide - known as laughing gas and used for pain relief - were detected in the Rosie Birth Centre. But inspectors said senior managers, aware of the problem for more than two years, has only advised staff to open windows where possible.
Across the entire trust, inspectors said staff shortages meant there was not enough cover on wards including critical care, with employees moved from ward to ward to make up shortfalls.
This meant staff sometimes worked in areas where they lacked training, while some rotas had empty spaces and others were filled with agency workers.
Inspectors also noted a "disconnect between what was happening on the front line and the senior management team".
Many patients were waiting for follow-ups, the CQC found. During the inspection, there was a backlog of 227 ophthalmology and 233 dermatology patients waiting for a call back and a total of 605 across all specialities.
The pressure on surgical services also meant routine operations were often cancelled and patients were waiting longer than the Government's 18-week target for treatment.
Former chief executive Keith McNeil, who resigned last week, has defended Addenbrooke's as "phenomenal".
"Everywhere across the country people would be very envious of the sort of results we get day in day out," he said.
"People's lives are saved every day by that hospital. I cannot see why anybody would want to describe it as inadequate."
But Prof Richards defended its report, telling the BBC: "The staff are extremely caring and extremely skilled, so there some very positive things in this trust but there are also some things that are going seriously wrong that need to be put right and need to be put right very soon."
He added: "The main feature is that I think they have lost their grip on some of the basics, particularly the basics of how to get patients through the hospital in a reasonable length of time and get them back out again, so the flow of patients through the hospital really works.
"When that goes wrong you then have to open more beds, now that obviously costs more money, but more importantly than that it also means that you dilute your staff, you then have to bring in extra agency staff and your staff are in the wrong place and that is what has happened at Addenbrooke's."
He added that improvements had already started to be made at the trust.
Placing a hospital in special measures is defined by health service watchdog Monitor, which carries out the act, as introducing "a set of specific interventions designed to improve the quality of care within a reasonable time".
In CUH's case it means a review of management, developing plans to improve both finances and patient care, and could also include the appointment of an external "improvement director".
Monitor also said it had the power to replace management if improvements were not made fast enough.
CUH Trust, which has more than 1,000 beds, is already under scrutiny by Monitor over its financial dealings.
The trust is running a deficit of £1.2 million per week and is predicted to overrun by at least £64 million this year.
Interim chief executive David Wherrett said: "Against a backdrop of increased demand and tighter resources, our services continue to be recognised nationally and internationally for their safety and patient outcomes.
"Patients are less likely to die here, be harmed, or catch a hospital-acquired infection than at almost any other trust in the country."