Having a health service without a workforce plan is "dangerous", a union in Northern Ireland said.
Antrim Area Hospital invited well-trained St John Ambulance volunteers to help keep patients company as they awaited emergency treatment on a busy New Year's Eve.
The Royal College of Nursing said it was an unprecedented move as part of a "crisis" created by a shortage of NHS nurses.
Its Northern Ireland director Janice Smyth (pictured) said: "This is heading only in one direction and in the absence of a workforce plan this is highly dangerous.
"Once broken it is not easily fixed."
She said the volunteers' role was limited to largely sitting with patients while they awaited attention and they had to be accompanied by registered nurses.
She said there were 1,500 nursing vacancies waiting to be filled, and they did not even have the staff to support the beds they had, never mind those waiting on trolleys during peak times like January.
"It is an unprecedented step and it is another sign our health and social care system is in crisis.
"We don't have enough nursing staff."
She said Antrim Hospital's director of nursing was left with an extremely difficult decision before calling on St John Ambulance.
"It was the least worst decision, people needing care, lots of trolleys and extra patients in wards."
St John Ambulance said its people were well-trained and such work was what it existed for.
A spokeswoman said its volunteers' actions on New Year's Eve were "nothing spectacular" and it was made clear across the UK that they attended emergency units to give support.
"The support is limited, it really is supporting patients, making tea and keeping them company."
Meanwhile, a social media poster said she waited many hours at the Royal Victoria Hospital Belfast's emergency department with an 81-year-old who had suffered a minor stroke-type event.
It was allegedly a prolonged period before the patient was given a trolley to sleep on.
Sinn Fein health spokesman Pat Sheehan said some measures taken by senior health staff to plug the gaps were not sustainable.
"The huge commitment and dedication shown by HSC (Health and Social Care) staff, particularly over this challenging holiday period, must be recognised and appreciated.
"Staff have again shown they are the HSC's greatest asset.
"A workforce strategy is needed to begin to address existing staff shortages and to ensure we retain the existing staff who continue to deliver vital health services under extremely challenging situations."
DUP Assembly member Peter Weir highlighted the absence of devolved government at Stormont.
"On her first day as health minister Michelle O'Neill stressed the priority she placed on reforming our health service to deliver for patients.
"Today however the former health minister plays the role of a disinterested observer as our health service faces major pressures, and our health service staff work tirelessly to deliver the very best service to the public."
The Health and Social Care Board said that from Christmas Eve to New Year's Day, 15,626 patients were treated in the main emergency departments.
This represented an increase of 4% (559 patients) compared with last year and a 14% increase (1,856) compared with 2015/16.
A total of 928 people had to wait longer than 12 hours to be seen, treated and either discharged or admitted to hospital.
A spokesman for the Board said: "Plans have been put in place across the health and social care system to manage increased pressures at this time of year.
"However, as a result of increased demand on top of an already very busy system, the level of complex and serious conditions, particularly amongst the growing frail and elderly population, the prevalence of flu and other respiratory conditions at this time of year, and the challenges of helping patients to return home after a hospital stay, some patients have had to wait more than 12 hours to be admitted to hospital.
"We fully understand the upset and inconvenience this causes to patients and their families and apologise to them for it.
"We can assure the public that anyone who needs to use an emergency department for urgent or life-threatening conditions will continue to receive access to safe, high-quality services from our highly skilled and committed staff."
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