WARNING: This story contains graphic content that may upset some readers.
Horrific video has emerged of an Australian teenager strapped into a mechanical restraint chair, wearing a ''spit hood'', as part of his punishment in a youth detention centre.
The disturbing footage, which aired on the ABC's Four Corners programme, was part of an investigation into the mistreatment and abuse of youths at the Don Dale Youth Detention Centre in Darwin.
The boy in the footage was identified as Dylan Voller, a 17-year-old boy who was a detainee at the centre.
He was allegedly abused numerous times over a five-year period from October 2010.
He is also one of six boys held in isolation cells at the detention centre, where they were teargassed in 2014.
Four Corners obtained footage of teens in 2014 at Don Dale Youth Detention Centre and again last year in the old Berrimah adult prison that replaced Don Dale.
In Don Dale, teens kept in the isolation wing known as the Behavioural Management Unit (BMU) were allegedly locked in tiny cells for almost 24 hours a day with no running water and little natural light.
Voller was handcuffed and hooded and strapped to a chair for two hours after he threatened to hurt himself while in the adult prison.
In the footage, guards ordered Voller to walk backwards into an isolation cell before asking the guards why his mattress was taken away.
Prison officers were heard saying Voller had misbehaved by chewing on his mattress.
The prison officers filmed him being strapped into the chair by his ankles, wrists, shoulders and neck while wearing a "spit hood" to stop him spitting on them.
He was left in the room for almost two hours by himself.
When the guards returned he was still in the chair with the restrictive spit hood still on.
Since he was just 11, Voller has been charged with offences including aggravated assault and robbery.
He is being held at Darwin's adult prison now. His lawyers claim he has been subjected to ongoing assaults and institutionalisation.
In more footage obtained by Four Corners from other alleged abusee, Voller was thrown across his cell, kneed and knocked to the ground, stripped naked and sent to solitary confinement. He was also held face down for three minutes in a hogtied position by one guard.
The programme also showed shocking footage of children being teargassed, which was described as a "riot" at the time by media.
It was previously reported that boys had escaped their cells in the isolation wing of the prison, and were threatening staff.
All six boys were exposed to the teargas. Five of the teenage boys were still locked inside their cells, and not all of them were misbehaving at the time to warrant such extreme discipline.
After the teargassing, the Don Dale Detention Centre was closed and all children were moved to the Berrimah adult prison.
Although the Northern Territory Government commissioned an independent report, NT children's commissioner Colleen Gwynne told Four Corners there were still issues with youth detention in the Northern Territory.
"They're being shackled to chairs a la Guantanamo Bay," barrister John Lawrence told the ABC.
"This is actually happening in Australia in 2016."
The NT Government's tear-gassing and "torture" of children in detention at Don Dale is a "national disgrace that demands a national inquiry", the Sydney-based law firm representing two of the youths said.
They're being shackled to chairs a la Guantanamo Bay. This is actually happening in Australia in 2016.
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Peter O'Brien, a lawyer representing two boys suing the NT Government for alleged detention centre abuse said: "The Four Corners programme on the horrific treatment of children has exposed a national disgrace that demands a national inquiry.
"A Royal Commission into the treatment of children in Northern Territory detention is essential to determine the extent and impact of the abuse, to determine why this abuse was allowed to occur, and who knew about it," he said.
"The abuse is chronic and appears systematic. Our clients have suffered at the hands of those charged to protect them," he added.
"The treatment of these children is a national disgrace. They are the most vulnerable members of society, and yet the footage shown on Four Corners reveals the most appalling behaviour being perpetrated against them."
On the ABC's Q&A programme, Australian's human rights chief Gillian Triggs called for a government inquiry into the facility.
"We certainly need some kind of government-based independent commission," she said.
Triggs said the footage of the detention centres was "extremely distressing".
"Sadly, I have never seen conditions of that kind and I have never seen people treated in that way. We clearly need some kind of investigation into this."
Correctional Services Minister John Elferrink said he had not seen many of the videos, including one where guards were saying "I'll pulverise the f***er" as a young man in isolation was yelling at windows.
"That demonstrates a lack of training," he told Four Corners. "When matters come to me I make sure they're investigated." Since 2014 the government has extended staff training from four days to eight weeks.
Lawyers and human rights activists have called for the facility to be shut down for good and called on the federal government to intervene.