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Juveniles inside one of WA's toughest jails have injured six prison guards during a violent stand-off that lasted 10 hours.
Saturday's chaos was sparked when two detainees at Casuarina Prison in Perth allegedly struck an officer in the head with a makeshift weapon, before stealing her keys.
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Authorities said 13 juvenile detainees assaulted the guards and damaged three buildings, climbing onto roofs and throwing debris and fire extinguishers.
One guard, aged in his 50s, needed to be taken to hospital with a broken foot.
The chaos unfolded at 4pm when two inmates outside allegedly hit a youth officer with a metal bar and took her keys to release others from cells.
Andy Smith from the WA Prison Officers' Union said he'd never heard of an incident like this in the state.
"Once a detainee gets a key it ceases to be a prison," he said.
The Specialist Operations Group was eventually called in, with the last inmate surrendering about 2.15 am.
The troublemakers were being held in the adult prison's controversial unit 18, which was set up for those too badly behaved for Banksia Hill Detention Centre.
But not all kept there are underage, which is something Premier Mark McGowan wants changed.
"When you turn 18 and you're a juvenile, unless there's some exceptional circumstance, you'll be transferred to an adult prison," he said.
But as Banksia Hill undergoes a major security upgrade it will be months before unit 18 is shut down.
9News understands the ring leader has a history of attacking officers, and had stolen pepper spray from one only days earlier.
They also put another female staff member in a headlock twice in the same day.
"The juvenile system is in need of a massive overhaul. We can't have them assaulting officers and then being released back into the system where they can do it again," Smith said.
The union predicts more drama unless staffing levels are urgently increased.
"Today Casuarina Prison is short 90 officers," Smith said.
"How can you run the biggest max security prison in the country 100 officers short?"
