Managers of the Royal Cornwall Hospitals Trust have been ordered to make urgent improvements to protect the safety of patients.
The Care Quality Commission found staffing levels inadequate at times in its emergency department during an inspection in June.
Surgery was rated good, but inspectors also found wards full with patients waiting for support systems to be arranged.
The hospital says is is already making improvements.
We have to accept the findings. They came at a time when we had particular issues with flow out of the department and they're right, that's not a great mix, having too many patients in the department and not enough staff can potentially raise safety concerns.
That was the key finding that we were reflecting on here in the Emergency Department. We're now moving to have 14 nurses on the day and 11 at night which is a significant change from a few years ago when it was 12 and 9.
Weston-super-Mare's NHS trust has been told it must improve by the health regulator, the CQC.
Although the trust, based at the town's General Hospital, was described as "caring", inspectors said patients waited too long to be assessed in A and E, while a shortage of consultants was putting strain on junior doctors.
When you've got that number of vacancies over a sustained period of time it makes life pretty tough. The doctors who are there are working hard but they're under consistent pressure in a way that's more severe than we've seen anywhere else.
The health watchdog has found Accident and Emergency care at Derriford Hospital inadequate - and the Trust overall as requiring improvementRead the full story ›
The Great Western Hospital in Swindon has been told it must improve staffing levels. It has also been ordered to improve cleanliness and infection control, and how it monitors the quality of its service.
It follows an inspection by the Care Quality Commission which found that some wards caring for frail, older people and the Day Surgery Unit did not always have enough experienced and skilled nursing staff on duty.
Campaigners for better care for the elderly have welcomed plans by the Care Quality Commission to use hidden cameras.
But there are concerns that authorities lack the power to deal with cases of abuse and neglect.
One man in North Devon says his concerns about care for his mother were ignored, as John Andrews reports.
A controversial plan to install hidden cameras to check for abuse in care homes is being considered by the industry's regulator. It follows undercover filming which showed mistreatment of patients at Winterbourne View near Bristol.
It's part of a consultation announced by the head of the Care Quality Commission today. Our political correspondent Bob Constantine reports.
Directors of care homes such as Winterbourne View near Bristol where patients suffered neglect could be held criminally accountable under plans announced by the Care Minister Norman Lamb:
Eleven care workers from the hospital near Bristol were sentenced last year for abusing and neglecting patients following an undercover television documentary.
We're not jailing but it would be unlimited fines and it will be for the awful cases.
If you break the fundamental standards that you have to comply with as a provider of care, and you are responsible for that, there are consequences, and I think that's what the public expect.
There's also a culture when awful things happen, there's a cover up, people get paid off, they get gagged from talking about it. That has to end.
These pay offs have to end and people at the top of the organisation should be held to account."
Scandals like Winterbourne View and Mid-Staffs have damaged confidence in our health and care system.
Part of our commitment to rebuilding that trust comes from making sure that people at all levels are held to account for failings when they occur.
Whilst there must be a sharper focus on corporate accountability, more needs to be done to ensure those responsible for leading a care organisation are up to the job.
I hope that providers and people who use services and their families will respond to this consultation as we look to take these proposals forward."
The Care Quality Commission has issued a formal warning to Avon and Wiltshire Mental Health Partnership over levels of staffing at Blackberry Hill Hospital in Bristol.