Northern Ireland's chief nursing officer, Charlotte McArdle, has said Northern Ireland emergency departments are "not in crisis".
However Janice Smyth from the Royal College of Nursing said there was a crisis and she was "very concerned".
In November the RQIA formally notified the health department there was a serious nursing shortage across hospital and community services.
Ms McArdle told the BBC there were "no quick fixes" to the current shortage.
She said ongoing initiatives to recruit nurses would continue.
She also revealed she had not visited any of the emergency departments over the holiday period but had given her support to nurses.
"My attendance at an already busy department department is taking staff away from their jobs which is caring for patients," she said.
She said the level of agency staffing was higher than wished but at the moment was necessary to keep services running.
Janice Smyth said the current staffing shortage was a crisis.
"Charlotte McArdle is very well across it and knows what needs to be done but as she said, these things are not easily fixed.
"Nurses are consistently going on duty to work on nursing teams where there are gaps and those are often filled by people who perhaps don't normally work in that area.
"More commonly, and more concerning, is what happens when nurses go on duty and some of those the gaps cannot be filled and they're left working short.
"Even when teams are fully staffed, the demands on nurses, means they may not be able to provide the care that they need to patients".
Ms McArdle paid tribute to the work of nurses and other medical staff who "continued to provide a first class service throughout the significant pressures being faced on a daily basis by the health and social care system".
Apart from the surge in demand, a lack of nurses has been among the aggravating factors on the health service in Northern Ireland.
Ms McArdle said she fully recognised that staffing levels "are a source of great concern to nurses".
"I want to assure them - and the public - that the issue is being actively addressed on a number of important levels," she added.
"The challenge is by no means unique to Northern Ireland - there is a nursing shortage right across these islands and there are no quick solutions - it takes three full years to train our high calibre graduate professional nurses."
She said the Department of Health and Health and Social Care staff were driving forward "a series of important workforce measures and initiatives".
- Increasing the number of pre-registration nursing student places funded annually from NI universities from a baseline of 650 places per annum in 2014/15 to 901 by 2017/18
- An international recruitment campaign which started in May 2016 and "is on course to meet the target of recruiting 622 nurses by March 2020"
- A regional nursing recruitment group leading work to streamline recruitment processes and encourage nurse retention
- An investment of £12m which Ms McArdle said had "increased nurse staffing levels in acute hospital wards"
Ms McArdle acknowledged the system is under pressure and staff "are being asked to work harder and harder in difficult circumstances".
"The way services are organised is out of date and not delivering the way we want it to and therefore existing capacity cannot meet the ever-rising demand," she said.
"Transformation of health and social care is the answer, and indeed is the only way forward - our nursing staff have a pivotal role to play in driving this change forward and I have every confidence that they will continue to step up and play their part in delivering this."