Spending on private nurses at NHS Grampian has soared by more than 2,700% in just five years.
Shock new figures show the health board spent more than £1.9million on stand-in ward staff in 2015-16 – up from just £70,000 in 2011-12.
NHS Highland’s spending on temporary nurses also rose by more than 200% in the same period.
Its bill in 2011/12 was £326,896 – and that had more than trebled to £1,017,756 in 2015-16.
Over the past five year’s NHS Grampian’s total bill for agency nurses was £3,825,000 and NHS Highland’s was £3,209,000.
Scottish Labour’s Anas Sarwar criticised the Scottish Government over the figures – claiming Health Secretary Shona Robison was “burying her head in the sand” over the staffing crisis in the NHS.
But the SNP administration at Holyrood said the number of nurses and midwives had increased since it came to office.
Health boards use agency staff “where gaps emerge” in the normal workforce.
NHS Grampian said stand-in nurses were only used in “exceptional circumstances”.
There are more than 2,200 nursing vacancies across Scotland, while the latest NHS staff survey found that only a third of health service staff think there are enough of them to do their jobs properly.
Mr Sarwar said: “We are in the middle of the biggest nursing crisis in the history of the NHS yet the SNP health minister appears determined to stick her head in the sand and deny a problem even exists.
“More than 2,200 nursing vacancies is a shameful statistic, leaving our dedicated but overworked and undervalued nursing staff under extreme pressure.
“This is not fair on staff and not fair on patients they are being asked to care for.”
North-east Labour MSP, Lewis Macdonald, said: “If you look at the number of vacancies in NHS Grampian, it is moving in the right direction.
“They were through the roof, but they are now coming down, which is a good thing.
“But clearly there is still a big gap and that is seriously concerning.
“When you combine the almost £2million spend on agency staff with the issues around medical recruitment, it points to a serious failure in workforce planning.
“The Scottish Government continues to underfund NHS Grampian and the consequences are increasingly clear.
“The two issues go together and show there is a real problem with the Scottish Government’s treatment of NHS Grampian.”
The cost of agency nurses varies depending on the type of work – but based on the Grampian figures the average is just over £26 per hour.
A senior nurse on an NHS salary earns on average about £15 per hour.
Ms Robison said agency staff accounted for only 0.4% of the NHS workforce, and the total spent on agency nurses and midwives was 11.3% lower than a decade ago.
She claimed there were now more than 2,300 more qualified nurses and midwives than when the government took office, and the number of training places in 2016-17 had risen for the fourth year in a row.
The minister added: “We know more needs to be done to reduce agency use.
“Earlier this year we launched a new initiative to drive down the cost and use of all temporary agency staff.”
An NHS Grampian spokeswoman said agency staff were used to keep wards working effectively and safely.
She added: “Where gaps emerge in our core staff complement we will look to our nurse bank.
“Staff on the bank are recruited to the same robust standards as other staff in NHS Grampian.
“Agency nursing is used only in exceptional circumstances where we cannot provide nursing cover from either core or bank staff.”
A spokesman for NHS Highland said: “We closely monitors use of agency locum nurses across all our services and are taking action to ensure agency usage is kept to a minimum.
“The reason for the increase in spending since 2011-2012 is primarily due to the Vanguard Theatre services at Raigmore Hospital.
“The Vanguard Theatre is a separately staffed theatre facility whose nursing costs are charged to the Vanguard agency.
“This accounted for approximately 70% of the total agency spend for nurses in NHS Highland in 2015-16.
“In addition, we are implementing a number of other programmes to continue to improve our recruitment and retention of nurses across NHS Highland to sustain a staffing model that minimises the use of agency staff.”