Patient safety could be compromised by a reliance on temporary staff to plug gaps in Northern Ireland's nursing and midwifery sector, a report has warned.
More than one in 10 registered nursing posts here were vacant by the end of last year, with £115m spent annually to cover shortages.
In some cases, up to £1,700 was paid to cover a single shift.
Spending on temporary staff has increased by almost 700% in a 12-year period, the Northern Ireland Audit Office found.
Comptroller and Auditor General Kieran Donnelly said: "The reliance on temporary nurses, particularly agency staff, has not only resulted in soaring costs, it also can compromise the quality and safety of patient care as staff are deployed in less familiar clinical settings.
"It is clear that this does not represent value for money."
Today's report examines the nursing and midwifery workforce within the Health and Social Care (HSC) and independent care sectors. It reviews whether the workforce is capable of dealing with future challenges and increasing demands on services.
Key findings include:
As of March 2019, 66,800 people were employed in the health and social care sector - a third (almost 22,500) in nursing and midwifery. Up to 3,500 nurses may also be employed in the independent care sector.
However, as demand on the local healthcare system has grown, so has reliance on temporary staff to cover shortfalls.
Between 2014 and 2019, the registered nursing vacancy rate increased from 3.2% to 11.5%.
The shortage of nurses and a recurrent funding gap of almost £40m have hampered efforts to recruit these staff.
The report also finds that a Department of Health decision to reduce the training budget for pre-registration nursing has contributed to the workforce shortages, with 732 fewer nursing training places created between 2011/12 and 2016/17, compared with 2009/10 levels.
Expenditure on temporary staff - from internal banks and external agencies - has increased dramatically, from £14.6m in 2006/07 to £115m in 2018/19 - a rise of 687%.
Today's report states the increase in agency costs, from £8.6m to £52m, has provided particularly poor value for money.
In 2018/19, trusts incurred costs of up to £1,700 for single nursing bank holiday shifts.
Three of the five trusts reported that, in 2018/19, they had paid hourly rates as high as £131 for non-contracted agency nurses.
Mr Donnelly said: "At a time when the focus should have been on growing the nursing and midwifery workforce, short-term savings were instead pursued.
"Substantially reducing the number of training places over a lengthy period has left the HSC and independent care sectors with an insufficient staffing pool to cope with the rising demand for care."
The report cites previous warnings from regulatory body the RQIA that nursing shortages were reducing staff morale, leading to higher sickness absence, and impacting on staff training, appraisal and supervision, which in some cases was leading to less effective patient care.
However, it does note significant action taken by the department to address staffing gaps.
This includes 746 pre-registration nursing places commissioned in 2016/17, which has increased to an average of 974 places between 2017/18 and 2020/21, with 1,210 places commissioned in 2020/21 alone.
Some 205 midwifery places were commissioned in 2019/20 and 2020/21, which is substantially higher than previous levels, it added.
A Department of Health spokesman said: "The Audit Office has acknowledged that 'important steps' are being taken by the department to respond to nursing workforce challenges. Its report confirms that nursing training levels have been 'significantly increased' in recent years, with an 'all-time high level' achieved this year.
"The Audit Office states that past "short term" decisions on nursing training places in previous years were taken in the context of wider funding pressures.
"Budgetary pressures remain significant for our health service and the wider public sector.
"While the use of agency staff is currently necessary to maintain stretched services, the Department fully accepts that the increasing agency expenditure is unsustainable.
"A big part of the answer is to transform the way services are provided - for the benefit of both patients and staff."