Information provided under the Official Information Act from the Bay of Plenty District Health Board showed that together, the board's three mental health units totalled 394 days operating over capacity in the year to May 9.
It said seclusion areas may be used for patients to sleep in if there was "absolutely no other alternative" with free access in and out for tāngata whai ora (people seeking health).
This only occurred in "extreme cases" when occupancy was "very high".
Seclusion rooms are designed for patients who may pose a risk to themselves or others.
Tauranga Hospital has two inpatient units - one for adults and one for older people - and Whakatāne Hospital has one adult unit.
Data for the year showed the highest occupancy rate for the Tauranga adult unit was 29 people - it is funded for 24 beds.
The highest occupancy rate for Tauranga's other unit was 13 patients - it is funded for 10 beds. The Whakatāne unit's highest occupancy rate was 14 patients and is funded for 10 beds.
The board was asked where patients slept when there were more patients than beds in the facility. It responded that treatment rooms, assessment rooms and "low stimulus areas" were used as bedrooms, as well as seclusion areas.
The management of which rooms were used was done by clinical staff who considered safety, how to best meet the specific needs of the tāngata whai ora and availability.
The New Zealand Nurses Organisation mental health nurses section chairperson Helen Garrick said it was "terrible" other rooms were being used for patients to sleep in.
"You're left with a situation where you either prematurely discharge somebody to create a bed or you bring the person in and you put them somewhere in that unit."
She said seclusion areas and assessment or treatment rooms were not "ideal" for "patient comfort, dignity and privacy".
Garrick said overcapacity in mental health units was "an issue throughout the country" and overcrowding was a "contributing factor" to assaults and violence occurring.
On June 3, the Bay of Plenty Times reported there had been 176 recorded assaults on mental health staff at the Bay of Plenty District Health Board's inpatient units between 2017 and 2021.
The most serious assaults included a staff member being punched in the eye and another punched in the throat.
Garrick said: "People need space to move around ... they need privacy, they need to be able to get away from other people if they're feeling distressed by something. And you can't do that in an overcrowded unit.
"You're actually squashed in together - and by that I mean the staff and the patients in those settings are all crowded into the same spaces.
"If you cram more people into these spaces and use other rooms ... then those rooms are no longer available for their purposes.
"If you've got no assessment rooms, for example, because you've had to convert them into bed space, then where do you do your assessment?"
Bay of Plenty District Health Board mental health and addictions business leader Jen Boryer said seclusion areas may be used for patients to sleep in when the ward was about 20 per cent over capacity, for example, 29 to 30 patients in a 24-bed unit. This depended on the "presentation and acuity of clients".
She said a seclusion room was designed to minimise "ligature and safety risks" for tāngata whai ora who were "very unwell and at risk to themselves or others".
When other rooms were used for patients to sleep in, "temporary bedding" such as mattresses were used.
Asked how DHB was addressing over-occupancy, Boryer said clinical assessment took place prior to admission, which looked at options for in-home or community-based care.
It had a project looking at ways to reduce the need for admissions or to expedite safe discharges for those in inpatient care by offering clinically supported accommodation in the community.
"This is looking at the gap analysis and options for future investment."
Funding for new adult inpatient units in Whakatāne and Tauranga was announced in January 2020 but this did not include an increase in beds, Boryer said.
Since then, a business case for a new Whakatāne unit was being presented to the Ministry of Health, requesting an increase in beds. In Tauranga, a business case reflecting "safety and ligature remedial work" had been submitted.
Mental Health Foundation chief executive Shaun Robinson said in his view, people sleeping in treatment rooms and seclusion areas was the result of underfunding in mental health over the past 10 years.
In the Lakes District Health Board, information received under the Official Information Act showed there were no days within the year to May where its mental health inpatient unit, Te Whare Oranga Tangata o Whakaue, was operating at over capacity.
The whānau room, which was used as an overnight stay facility for whānau from out of town, could be used for extra capacity if required.
Where to get help: If it is an emergency and you feel like you or someone else is at risk, call 111.