SYDNEY, Australia - Australia's prime minister ordered a sweeping investigation Tuesday into alleged abuse at a juvenile detention centre after video emerged of Aboriginal teens being tear-gassed, stripped naked and shackled to a chair.

Prime Minister Malcolm Turnbull said he would launch a Royal Commission - Australia's highest form of inquiry - and suggested that there had been an institutional coverup of the scandal. Rights groups, however, scoffed at the coverup claim, saying officials had ignored evidence of abuse in the corrections system for years.

The footage, which aired Monday on the Australian Broadcasting Corp.'s investigative program "Four Corners," was filmed largely at a youth detention centre in the Northern Territory city of Darwin between 2010 and 2015. Its release triggered a national uproar, with officials from the local level all the way up to the prime minister denying they had ever previously seen it.

"We are determined to get to the bottom of this, we're determined to examine the extent to which there has been a culture of abuse and, indeed, whether there has been a culture of a coverup," Turnbull told reporters. "Why was this abuse, this mistreatment, unrevealed for so long?"

When the tear gas incident occurred in 2014, officials said guards used the chemical to subdue six teens who had staged a riot. But closed circuit television and video footage filmed by staff at the centre appears to show that the tear gas was used after just one teen escaped his cell, while the other five remained locked in their cells. The guards are heard laughing as the teens cough and cry after multiple shots of tear gas were fired into the isolation wing where they were housed. One of the detainees can be heard saying he can't breathe.

In another video, a guard is seen picking up a 13-year-old and hurling him across the room onto his bed. The same boy is also seen in footage from a different Northern Territory detention facility being stripped naked and held face-down on his bed by three guards after he apparently threatened to hurt himself. In yet another instance, the teen was shackled to a restraint chair with a hood placed over his head, before being left alone for hours.

Human rights activists accused the government of ignoring the issue until it became public because the teens involved were indigenous. The Northern Territory has the highest rate of youth detention in the country, and 97 per cent of its juvenile detainees are Aboriginal.

"Amnesty International has repeatedly raised concerns of abuse of children being held in youth detention centres in the Northern Territory," Julian Cleary, Indigenous Rights Campaigner at Amnesty International Australia, said in a statement. "As this program shows, these are not isolated incidents."

Indigenous Affairs Minister Nigel Scullion said the footage was particularly shocking because the guards involved appeared cavalier about their actions. He said the officers should face criminal charges.

"They knew ... that their behaviour was clearly not right, it was evil, but they also knew they had absolutely no chance of that being a problem to anyone," Scullion told reporters in Canberra, the capital. "Such was the culture of coverup, such was the culture of brutality."

The Don Dale Youth Detention Centre has been the subject of complaints for years. Last year, a review of the facility by the Northern Territory Children's Commissioner found an excessive use of solitary confinement and inappropriate use of restraints.

Northern Territory Chief Minister Adam Giles said he had never seen the footage before it aired on Monday, also blaming a coverup within the corrections system for the government's previous inaction. He said he had removed Northern Territory Corrections Minister John Elferink from his position on Tuesday.

"I sat and watched the footage and recognized horror through my eyes," Giles told reporters in Darwin.

But Priscilla Collins, CEO of the North Australian Aboriginal Justice Agency in Darwin, said officials knew about the footage for years.

"There is no coverup. They've been fully aware of what's been going on," Collins told reporters. "The reports show it, the children's commissioner's report shows it. They had access to the footage."

Australia has a checkered history when it comes to its treatment of child detainees. Human rights groups have long criticized the country for its indefinite detention of asylum seekers and their children in remote, offshore immigration detention camps; the government's own human rights watchdog last year found that the policy violates international laws. The United Nations Convention on the Rights of the Child, to which Australia is a party, states that the detention of children should only be a measure of last resort.

The Royal Commission is expected to begin holding hearings in September, with a final report due to be released early next year, Turnbull said.