A 17-year-old has become just the second child on record to die in youth detention in WA.

WARNING: This story discusses incidents of self-harm. Aboriginal and Torres Strait Islander readers are advised that this article contains the name and image of a person who has died.

The boy, who authorities said "identifies as Indigenous", was found unresponsive in his cell on Thursday evening at the Banksia Hill Detention Centre.

Here's what we know so far:

How long had the boy been in custody?

Corrective Services Commissioner Brad Royce told journalists the teenager had arrived at the detention centre on August 27, just two days before he died.

The ABC understands he had been in detention previously, and in the notorious Unit 18 last December.

Unit 18 is the juvenile wing of Perth's adult maximum security Casuarina Prison, established to house detainees from Banksia Hill considered too dangerous to manage at that facility.

It was where 16-year-old Cleveland Dodd self-harmed in October last year, becoming WA's first recorded death in juvenile detention.

Now, less than a year later, there has been another. 

Commissioner Royce said the boy had been "intoxicated and potentially had been taking illicit drugs as well".

Because of this he was placed on the 'At Risk Management System', for people who required more frequent observations.

It was said he was "given healthcare and access to clinical support".

What happened on Thursday?

On Thursday, just after lunch, the boy was transferred to a general unit named Turner, presumably because he was no longer deemed to require such close observations.

Commissioner Royce said there were other people he knew in that unit, and he was out of his cell for some hours.

Some time after 6pm he went back into his cell.

"Over the course of the evening we know he was checked 10 times by my staff," Mr Royce said.

During that time he made some calls to staff on an in-cell intercom but nothing that rang alarm bells.

"On the 11th occasion [he was checked], just prior to 10pm he was found unresponsive."

How did staff respond?

Commissioner Royce said staff raced to the cell, including the on duty nurse, and performed CPR.

St John Ambulance said they were called at 10.01pm and arrived at 10.10pm.

But he couldn't be revived and was declared dead at the scene.

Commissioner Royce said he was advised of the boy's death within the hour and spent most of the night at Banksia Hill.

He said he had viewed vision taken from the body-worn cameras of staff on duty, and was satisfied the appropriate action had been taken.

There were 17 staff on duty at Banksia Hill at the time, as well as the nurse, to supervise 57 detainees.

What happens next?

Premier Roger Cook said the boy's death would be the subject of a coronial investigation, and police were preparing a report.

An internal investigation will also be conducted.

Corrective Services Minister Paul Papalia said eight Aboriginal elders and members of the Aboriginal Services Unit were supporting inmates at Banksia Hill on Friday.

The Education Department's crisis response team had also been deployed.