A lack of staff, ambulances queuing outside, and patients treated in corridors - that was the scene health officials were met with when they paid an unannounced visit to the county's busiest emergency department last month.

Inspectors from the Care Quality Commission (CQC) hit the Norfolk and Norwich University Hospital (NNUH) with a warning known as a section 29a notice.

And inspectors said said it must make 'significant improvements' after a recent visit to the emergency department, clinical decision unit, and the urgent care centre

Since then, officials from south and north Norfolk clinical commissioning groups (CCGs) paid an unannounced visit on December 15..

Documents released ahead of CCG meetings this week said they found 'unfilled vacancies across both the medical and nursing teams were having a significant impact on the department with consultant and nursing vacancies'.

They said there seemed to be progress being made in recruiting nurses, but on the day of the visit the department was one consultant down.

They also saw up to 17 ambulances queuing and while the department was busy, they saw 'some areas [...] remained relatively under-utilised'.

Inpatient units were reportedly asked to take two patients more than their normal capacity to support the pressure at the front door.

And building work on the new older person's A&E, children's unit, and a redesigned area for those with mental ill health meant the department 'appeared under strain' and some patients were cared for in corridors.

However, patients told inspectors 'despite the long waits that their care had been excellent, they reported staff to be caring and supportive'.

The CQC also visited the end of life services and theatres, with a full report expected next month.

A NNUH spokesman: 'There was some limited disruption while we were changing the building to create the older people's emergency department (OPED) which opened before Christmas. The CCG was aware of this and it is disappointing to read we are being criticised for improving the environment for our patients.

'The NNUH is the busiest hospital in the east of England on some days. We have seen up to 180 ambulances a day coming to NNUH and when a large number arrive at the same time it does create pressure for our service and then we use escalation areas. We are working closely with all our colleagues at the CCGs and social care to deal with this huge demand.'

The spokesman added the number of all staff, including registered nurses, at the hospital was at an 'all time high'.

What is a section 29a?

The warning from the CQC is issued under section 29a of the Health and Social Care Act.

CQC guidance said they are given when they 'identify concerns across either the whole or part of an NHS trust or NHS foundation trust and we decide that there is a need for significant improvements in the quality of healthcare'.

It added: 'This includes concerns that are probably systematic and affect the entire system or service rather than being an isolated matter and that result in the risk of harm or actual harm.'

Inspectors can also set a timescale within which problems should be fixed.

They will return for another inspection to check on progress.