A patient died at a Kent hospital as a "direct result of overcrowding and short staffing", a leaked letter seen by BBC South East has claimed.
The Royal College of Nursing (RCN) said patient care and safety at the William Harvey Hospital, in Ashford, was "severely compromised" last year.
Senior RCN officer Millie Simms wrote that nurses in the A&E department were working in "atrocious conditions".
East Kent NHS Trust said the "serious concerns" were being addressed.
However, Dr Peter Carter, the trust's interim chair, refuted the RCN's claim that the death of a patient could have been avoided, saying it had been due to "natural causes".
The letter was written on 2 October to Dr Sally Smith, the chief nurse and director of quality at the hospital, but it has only just been revealed to the BBC.
Dr Carter said the NHS locally and nationally was "under huge pressure" and the RCN had raised "some serious concerns".
"It's a long term problem in east Kent, which will not be solved in the short-term," he said.
He conceded that staff had been under a "huge strain", including over the Christmas and New Year period when the hospital was faced with "unprecedented levels" of patients.
"They had to be cared for somewhere... although they were on trolleys, they were cared for safely."
Dr Carter said the A&E department now had 12 additional nurses, a new specialist, and five more doctors.
In the letter, Ms Simms wrote that staff were "overworked, exhausted, demoralised and even ridiculed", with nurses forced to care for patients in corridors without monitors, oxygen or "any form of equipment".
"Last week a patient was reported missing from the unit... although the patient was found, sadly not in time as he was deceased, this traumatic incident has had a profound impact on the nurses.
"They believe this was a totally avoidable incident and is a direct result of the overcrowded unit, short staffing and unsafe conditions," she said.
The A&E unit has a capacity for 35 patients but the RCN said nurses were regularly dealing with upwards of 80 patients.
"In my experience... I have never come across such atrocious conditions where nurses are expected to deliver care," she said.
Speaking on Wednesday, RCN regional director Patricia Marquis said the situation at the hospital was "the same if not worse than at that time".