Former Western Australian premier Colin Barnett has condemned the conditions in the state's notorious Unit 18 as "bordering on torture".

Mr Barnett told The West Australian the treatment of children in the unit, which is within a maximum security adult prison, is "clearly abusive".

"Those young people, despite the offending they've done, are in small cells and experiencing 20 hours solitary confinement on a continuing basis," he said.

"To me, that is clearly abusive of anyone, but particularly of underage people, children, if you like, legally and I think it's actually bordering on torture."

Mr Barnett said he was driven to speak out by the deaths of two children in WA's youth detention system; 16-year-old Yamatji boy Cleveland Dodd in Unit 18 in October, and a 17-year-old in Banksia Hill last month.

Mr Barnett, a former Liberal MP who served as premier from 2008 to early 2017, said the treatment of children in detention in WA would ultimately stain the state's reputation on the world stage more severely than the destruction at Juukan Gorge.

"This is a sort of abuse of people that you see in undeveloped, backward nations and totalitarian states and so on," he told The West.

"This should not be happening in Australia, and certainly not in Western Australia.

"The fact that there had not been a suicide of any youth in the justice system prior to this, and there have been two in a year, is a great shame to Western Australia."

The former Premier said he was shocked by the silence of Labor MPs, with not one speaking out about the ongoing failure of the system on the government's watch.

"What I would like to see, I would like to see some of our members of Parliament from all parties that have spoken about justice issues, and, you know, suicide and so on at length," he said.

"So many left-of-centre politicians, obviously on the Labor side, and some Liberals speak out on those sorts of issues, but I haven't heard anything.

"Surely, there are some people in the West Australian Parliament, prepared to speak out — that's the only reason I am because I'm just frustrated in hearing nothing about it."

On Monday, WA Liberal leader Libby Mettam said a Liberal government would close Unit 18 as a matter of priority if elected.