A vulnerable teenager is living alone in a hotel despite attempting suicide two weeks ago.

The 16-year-old has been in and out of residential care since he was 12 but had been placed in a Dunedin hotel this week due to a shortage of residential care facility beds.

His distraught mother contacted the Herald, fearing her son was a danger to himself and people around him.

The Ministry for Vulnerable Children (MFVC) says the hotel placement is a "last resort" but the Children's Commissioner has labelled the short-term accommodation "not good enough".

The Herald isn't publishing the names of the mother or the son to protect their privacy.

The boy started acting out and becoming aggressive aged 9, and was removed from the family home aged 12 to protect other children living there.

He's been diagnosed informally with Asperger's by one doctor but other doctors have disagreed.

Two weeks ago he attempted suicide and was hospitalised, his mother said.

Doctors gave his mother a glimmer of hope, saying they would keep him in a secure mental health unit for five days to properly assess his mental health.

"We were like, 'Oh my gosh, that's so amazing, thank goodness'. We were so relieved that they were finally going to do something."

But the next day he was discharged after the doctor on call decided his suicidal crisis had ended, the mother said.

On Tuesday, the MFVC checked him into a hotel, telling his mother he could be there up to a month, she said.

"The longer you leave him to his own devices, the more it can get pear-shaped and things can go wrong," the mother said.

The teenager had to call his social worker three times a day, his mother said.

The mother felt her son was set up to fail.

"He's quite well known to the police in Dunedin. He's threatened people with knives, he's threatened himself with knives.

"It's been a hellish eight years of trying to get help for him. Nobody wants to listen, nobody wants to put down on paper what he has.

"So that means there's less resources and less help for him. I'm not angry at the social worker, because obviously this has come from his boss. But I'm so pissed that this is happening."

MFVC deputy chief executive Allan Boreham said young people were only placed in motels in "exceptional circumstances".

"In the case of this young man, the accommodation being used is definitely a last resort and is an interim arrangement while a longer term placement is found."

The decision would have been made by the boy's social worker, their supervisor, and a manager. A young person's safety was "of paramount concern" when placing them in a motel, Boreham added.

He did not know how many children were in similar circumstances.

Children's Commissioner Judge Andrew Becroft said anecdotally he was hearing more children with mental and behavioural issues were placed in inappropriate environments, due to a shortage of facilities. But that was an explanation, "not an excuse".

"We've got to the stage where a small group of very behaviourally-disturbed and challenging young people need much better facilities than we appear to have in New Zealand," he said. "We need to face the issue and respond pretty quickly."

If the boy had made another suicide attempt that emphasised how inadequate those short-term arrangements were, he said.

"I have no illusions how demanding and tough it will be to provide that sort of expert care facility but nothing less than that is required in a civilised community."

Where to get help:

• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• Samaritans 0800 726 666
• If it is an emergency and you feel like you or someone else is at risk, call 111.