Exhausted front-line staff at Auckland City Hospital have taken the unusual step of writing directly to management to warn of the danger posed by chronic staff shortages in the emergency department.

A formal document earlier this month signed by 150 staff, including doctors, nurses and healthcare assistants, said "safe staffing levels" were "consistently breached", exposing staff and patients to unacceptable risk.

Health New Zealand Te Toka Tumai Auckland told RNZ it has successfully recruited staff for all vacant positions in the emergency department and was working on other strategies to relieve the pressure.

However, staff nurse Nico Woodward - a Nurses Organisation delegate - said even when the emergency department (ED) and neighbouring clinical decision unit (CDU) were fully staffed, there were still too many patients for them to treat properly.

"We'll go almost weeks without dipping below 100 percent capacity, which even when we're fully staffed, the pressure is immense."

ED staff decided to escalate their concerns in a formal way after repeatedly filing "incident reports" with no tangible result.

"Submitting incident reports don't seem to be doing much other than creating paperwork for us," Woodward said.

"People are missing breaks, they're not able to take leave, we've got higher number of patients we're looking after, multiple sick calls, those sick calls aren't being covered, leaving staff having to pick up the pieces of what's left behind."

The problem had become especially acute in the last six months, with the emergency department hitting "nearly 200 percent occupancy" in May and continuing at a high level throughout winter, he said.

In a written statement, Dr Mike Shepherd, the group director of operations for Te Toka Tumai Auckland, acknowledged "that at times staffing in our ED/CDU has been very challenging, especially over the past six months".

"A number of factors have impacted on the daily running of the unit, and these include high demand, staff vacancies, staff turnover and sick leave.

"We have been providing staff from across the hospital to support, and have either implemented or are working towards implementing, a range of short and longer term solutions to help alleviate the challenges."

Those included having "successfully recruited" to fill all vacant positions in ED/CDU as well as recruiting for positions across the hospital, increasing nursing staffing in areas of pressure and putting other measures in place to ensure appropriate staffing levels for each shift.

"We would also like to assure the public that we are here for them and if they or their loved ones need urgent hospital-level care, they will receive it."

However, Woodward said front-line staff wanted management to commit to the agreed acute care ratio of one nurse to four patients.

"We're not being unreasonable, that's just sticking to the agreed model of care."

They want clinical staff redeployed from other roles in the hospital when the ED gets too busy, or for the hospital to close beds.

This story was originally published by RNZ.