The Northern Territory Corrections Commissioner has told a press conference that children are held in isolation for a maximum of 24 hours in youth detention, contradicting figures provided by his own department to Four Corners last week.

In a media response to the program, NT Corrections told Four Corners that children have been held in isolation on 72-hour placements on 22 occasions since January 2015.

On another 186 occasions children were held in isolation on 24-hour placements.

But this afternoon Acting Commissioner Mark Payne told a press conference a 24-hour maximum was in place.

"A number of children have been the subject of 24-hour placements. Certainly nothing in line of what we saw on the Four Corners program last night," he said.

Last night's Four Corners program revealed shocking vision of youth detainee Dylan Voller being repeatedly stripped and assaulted over three years while being kept in solitary confinement.

The 17-year-old was one of six boys tear-gassed in Darwin's Don Dale Youth Detention Centre in August 2014, after they had been kept in isolation for between six and 17 days.

Four Corners also obtained video of Dylan Voller being held in isolation and strapped into a mechanical restraint chair in March last year after threatening to self-harm.

"It is in line with the legislation under Section 153 Subsection 5 of the Youth Justice Act where a child needs to be held in a specific form of detention, that is an isolated detention, for the protection of other children or the protection of staff," Mr Payne said.

"They're held in the detention, in that isolation, for up to 24 hours. But as soon as a child's behaviour has modified to the extent that they are not at risk of harm to other detainees or staff members, they're released."

When asked how long children could be held in the cell for, Mr Payne replied:

"For a maximum of 24 hours. Maximum of 24 hours."

Twenty-four-hour placements can be enforced by the superintendent of the detention centre, while the approval of the Commissioner is needed before a child can be isolated for up to 72 hours, according to the Youth Justice Act.

Figures provided by the Corrections Department to Four Corners show isolation placements reached a disturbingly high peak in June 2015, with a total of 720 hours spent in isolation by children. Eighteen of them were 24-hour placements, and four were 72-hour placements.

In April 2015 alone, children were placed in isolation for 72 hours on six occasions.

The department said the use of isolation placements had declined this year due to better staff training and recruitment.

Northern Territory Chief Minister Adam Giles admitted there has been a "culture of cover-up" in The Northern Territory juvenile justice system, and said the Territory Government would work with the royal commission announced by Prime Minister Malcolm Turnbull today.

"All currently-held video footage or CCTV footage held by the Corrections agency has been ring-fenced," he said.

"The special investigations unit within Corrections is ensuring that that video footage will not be gotten to or tampered with, and will be made fully accessible to both police and to the royal commission of inquiry."