Nurses at Christchurch's Hillmorton Hospital say they are worried that safety problems are putting off new-entrant nurses from working at the facility.
Mental health nurses at the hospital's Adult Acute Inpatient Unit say they are frequently assaulted, and have blamed Canterbury District Health Board management for not taking the issue seriously.
A security guard has been put on the wards, and a working group is now looking at potential solutions.
A nurse, who asked to remain anonymous, told RNZ that staff are worried safety problems, and subsequent media coverage, could put off new nurses from wanting to work at the unit, which they said already struggled to fill vacancies.
"The gaps are being filled day-to-day, however the longer term is looking bleak," they said.
New nurses are placed at the facility as part of the New Entry to Speciality Practice Mental Health and Addiction Nursing programme, or NESP.
"The hospital has always been reliant on them to fill gaps," the nurse said. "It seems that a chronic staffing shortage may be just around the corner."
The Canterbury DHB said application numbers for NESP were similar to last year, and it was not worried.
They said that, as of today, it had two people confirmed and was waiting for confirmation from six more.
This time last year it also had two people confirmed and was waiting for confirmation from eight new nurses.
"We would generally not expect to see large numbers of inquiries this early in the NESP process," a spokesperson said.
"[The] Canterbury DHB is not concerned with numbers at this early stage in the process."