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Guard suffers 'fractured skull' in WA youth prison riot

A guard has suffered a suspected fractured skull after being hit by objects allegedly thrown by youth detainees at Perth's Banksia Hill detention centre.

Seven detainees climbed fences and rooftops on Monday after absconding from activities outside of their cells.

They allegedly ripped pieces of masonry and metal off the facilities and threw them at youth custodial officers, four of whom were injured.

The disturbance was brought under control by Special Operations Group officers and no detainees were injured, Western Australia's Department of Justice said.

Premier Mark McGowan has lashed out at the "thuggish" behaviour which he said had left one officer requiring surgery for a suspected fractured skull.

One of the detainees involved had turned 18 while in custody, the premier said.

He said the government would examine whether detainees should be moved out of Banksia Hill once they turned 18 and placed in an adult prison.

"We're going to have a very close look at those 18-year-olds ... because they're adults and they're in there leading juveniles astray," he told reporters on Tuesday.

"If you're going to climb on the roof as an adult and throw things at youth custodial officers then you can go to adult prison, in my view."

A Department of Justice spokesman told AAP courts were able to consider transferring detainees to adult prisons once they turned 18 if they had a "substantial" period to serve or if they posed a risk to the safety or welfare of others.

Mr McGowan acknowledged Banksia Hill was still experiencing staff shortages which sometimes restricted out-of-cell activities.

But he said there was no excuse for the "appalling" behaviour of some detainees.

"I'm sick of the excuse making. The excuse making goes on and on and on by some people out there who always say it's the government's fault," he said.

Department officials earlier this month conceded they did not have reliable data recording out-of-cell hours at Banksia Hill during the last financial year.

WA's Supreme Court last year found a teenage boy had been unlawfully locked in his cell for at least 20 hours per day on 26 occasions over six months.

A class action launched in the Federal Court on behalf of past and present detainees alleges a teenage girl with autism was confined for up to 23 hours a day.