An external review is underway after Chelsea Brunton went missing from Palmerston North Hospital and was later found dead.

The death of a 21-year-old who went missing from Palmerston North Hospital's mental health ward is under review.

Chelsea Brunton was found dead in a suspected suicide on May 10 at a residential property in Palmerston North, four days after she went missing from the hospital's ward 21.

Brunton had to leave the hospital grounds to have a cigarette. It was from one such unsupervised trip that she never returned.

Health minister Dr Jonathan Coleman said an external review, initiated by MidCentral District Health Board, was under way in relation to Brunton's death.

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The matter had also been referred to the coroner.

Ministry of Health director of mental health Dr John Crawshaw would be kept informed and would follow up any outcomes, Coleman said.

Crawshaw said all DHBs provided mental health services and all had non-smoking policies.

However, they did have a provision to allow patients to smoke in certain areas, including outdoor spaces.

"The ministry has supported DHBs to be smokefree, but recognises they also have a commitment to ensure the safety of individuals under their care.

"Decisions about how DHBs operate, including policies around being smokefree, are operational issues for individual DHBs."

Shaun Robinson, chief executive of the Mental Health Foundation, said it supported measures to reduce the prevalence of smoking and believed mental health services should work to make all facilities smokefree.

"Clients of the mental health system frequently increase the rates at which they smoke, or take up smoking, which can exacerbate conditions and interfere with the effects of medication.

"Research shows maintaining smokefree mental health facilities generally improves management outcomes, with fewer violent incidents, incidences of self harm and suicide related acts, and discharges against medical advice."

WHERE TO GET HELP

Lifeline (open 24/7) - 0800 543 354

Depression Helpline (open 24/7) - 0800 111 757

Healthline (open 24/7) - 0800 611 116

Samaritans (open 24/7) - 0800 726 666

Suicide Crisis Helpline (open 24/7) - 0508 828 865 (0508 TAUTOKO). This is a service for people who may be thinking about suicide, or those who are concerned about family or friends.

Youthline (open 24/7) - 0800 376 633. You can also text 234 for free between 8am and midnight, or email talk@youthline.co.nz.

0800 WHATSUP children's helpline - 0800 9428 787, Open between 1pm and 10pm on weekdays and from 3pm to 10pm on weekends. Online chat is available from 7pm to 10pm every day at www.whatsup.co.nz.

Kidsline (open 24/7) - 0800 543 754. This service is for children aged 5 to 18. Those who ring between 4pm and 9pm on weekdays will speak to a Kidsline buddy, who are specially trained teenage telephone counsellors.

Your local Rural Support Trust - 0800 787 254 (0800 RURAL HELP)

Alcohol Drug Helpline (open 24/7) - 0800 787 797. You can also text 8691 for free.

For more information, contact the Mental Health Foundation's free Resource and Information Service on 09 623 4812.