Hospitals are putting contingency plans into action as the latest Covid wave hits staffing numbers.
Wastewater trends show community cases are still rising and there are 336 patients in hospital with the virus nationwide.
Te Whatu Ora's director of hospital and specialist services Fionnagh Dougan said as the wave hit the community, hospitals were experiencing an increase in sick staff too.
Sometimes that included small clusters within specific teams or services, she said.
"In those instances, staffing is managed according to usual practice by bringing in additional resources where possible and making use of the willingness of staff to alter their rostered days off at short notice," she said.
But that language has annoyed the union, the Nurses' Organisation.
Its president Anne Daniels said last minute shift changes should be a last resort, rather than a core part of Te Whatu Ora's plan.
"Willing is one thing, whether they should even ask for that is another," she said.
Working sudden or extra shifts could increase fatigue which was bad for the wellbeing of nurses and increased the risk of mistakes, she said.
Te Whatu Ora was supposed to have systems in place to make sure they could cover illness.
"The fact they are asking nurses to change shifts every five minutes, doesn't reflect that their systems are working," Daniels said.
As with all Covid waves, the latest one was showing up how short staffed the health system is, she said.
Te Whatu Ora's Fionnagh Dougan said it did have systems in place to make sure there were enough staff all year, including during illness peaks.
"Any impact on hospital operations and the delivery of care has been well managed by local teams," she said.
She thanked staff for their flexibility and understanding, and said members of the public who needed hospital level care would get it.
RNZ requested exact staff illness numbers from Te Whatu Ora but was told that could only be answered by an Official Information Act process.
That would have likely taken weeks or months to answer.