Shocking video showing a 17-year-old boy being strapped into a mechanical restraint chair in the Northern Territory in March 2015 has been obtained by Four Corners.

Key points: Vision shows repeated stripping, assault and mistreatment of a boy

Vision shows repeated stripping, assault and mistreatment of a boy Boy transferred to adult prison, strapped to chair for almost two hours

Boy transferred to adult prison, strapped to chair for almost two hours His treatment in Youth Detention was the subject of a confidential investigation by NT's former children's commissioner

It is part of a chilling catalogue of vision released for the first time showing the repeated stripping, assault and mistreatment of the boy, who was one of six children tear-gassed at the Don Dale Youth Detention Centre in Darwin in 2014.

The boy in the chair is Dylan Voller, who was a detainee at the Youth Detention Centre in Alice Springs at the time.

The footage, along with other instances of mistreatment highlighted on Four Corners, prompted Human Rights Commissioner Gillian Triggs to call for a formal inquiry.

WARNING: This story contains graphic images.

On the day of the incident, he was transferred to the adult prison and strapped into the chair for almost two hours after threatening to hurt himself so that he would be taken to hospital.

In the vision, Mr Voller, who is handcuffed and hooded, is being ordered by guards to walk backwards, hunched over, into an isolation cell before asking the guards why his mattress was taken away, telling them he has been treated like a dog.

Prison officers on duty can be heard saying Mr Voller had misbehaved by chewing on his mattress and threatening to break his hand.

Guard: "You just can't put toilet paper everywhere, you can't rip your, you can't start chewing on your mattress. You can't do that stuff, you know that." Dylan Voller: "You can't lock me in here, bruz." Guard: "Unfortunately you've put yourself in here by going at risk."

....

Guard: "Might get the restraint chair possibly as well." Voller: "I don't want the restraint chair bro."

...

Voller: "Where's my f***ing mattress? I'm not a dog to you." Guard: "You need to settle down."

...

Voller: "I'm going to break my hand anyway." Guard: "Why are you going to break your hand?" Voller: "So I can go to hospital … (inaudible)." Guard: "Well you won't go … I doubt very much you'll go to hospital." Voller: "I'll snap my bone through my skin."

...

Guard: "Alright, well I'll just give you the heads up, grab the restraint chair, we are going in the restraint chair."

Next, guards record the boy being strapped into the chair by his ankles, wrists, shoulders and neck while wearing a spit hood.

The 17-year-old, who is known to spit on guards, does not resist and is left in the room for almost two hours.

When guards return he is still in the chair and appears to have been wearing the hood throughout the ordeal.

Guard: "How are we going?" Voller: "Good." Guard: "Are we a lot calmer?" Voller: "Yeah." Guard: "How are you going to spend the rest of your night? Nice and quiet? Not much fun hey?" Voller: "Nah." Guard: "What we have to do just so you know you are going to be cuffed to the rear this time? Your hood will … ". Voller: "… My wrist doesn't twist that far." Guard: "We will see, we aren't trying to hurt you it's just easier that way because you've obviously spat on staff already." Voller: "Yeah but my wrist doesn't twist (inaudible)." Guard: "Have ya? Alright I'll give you that leeway yeah? Don't make me regret it. Yes? Alright?" Voller: "Yeah."

Mr Voller has been in and out of detention centres around the NT since he was 11 years old. He has been charged with numerous offences including aggravated assault and robbery.

Now 18, he is being held at Darwin's adult prison. His lawyers say Mr Voller is the victim of repeated assaults and institutionalisation.

Vision obtained by Four Corners shows the boy being thrown across his cell, kneed and knocked to the ground, repeatedly stripped naked and also kept in solitary confinement.

Four Corners has learned his treatment in youth detention was the subject of a confidential investigation by the former NT's children's commissioner, Dr Howard Bath, which has never been made public despite the government being urged to act in 2012.

Mechanical restraint chairs necessary: Government

Earlier this year, after the video was filmed, the Northern Territory Parliament moved to amend the Youth Justice Act to ensure "that modern mechanical devices of restraint or advancements in technology" could be legally used on children.

In Parliament, NT Corrections Minister John Elferink said the restraints were necessary.

"I acknowledge that the proposed amendments may incite commentary from legal and youth services professions as to the perception that mechanical devices will be used to excess or in such a way that is not appropriate to the risk posed by young people in detention," Mr Elferink stated in Parliament.

"I make no excuses for the proposed amendments. They are crucial in providing detainees, members of staff at youth detention centres and the public with greater safety and security."

"They are consistent with this government's priorities regarding young people in the justice system."

Restraint chairs like 'Guantanamo Bay'

Barrister John Lawrence told Four Corners the amendments are "poison".

"We're talking about kids that are being shackled with handcuffs on their ankles, their wrists, their waist areas. They're being shackled to chairs," he said.

"One of them has had the experience of sitting in one for just under two hours with a spit hood over his head, a la Guantanamo Bay.

"This is actually happening in Australia in 2016."

A NT Government spokesman told Four Corners restraint chairs are only used at adult correctional centres and have only been used once on youth detainees.