West Australian Premier Mark McGowan has described an attack on guards in the youth wing of Casuarina Prison overnight as appalling and shocking.

A female guard was attacked by an inmate with a metal object during supervised recreation time on Saturday afternoon.

It’s understood she was struck in the head.

The woman then had her set of keys to the accommodation areas stolen, with the detainees freeing others before climbing onto the roof and damaging property.

A total of seven guards were injured during the unrest, with one suffering a broken foot.

Speaking at a press conference on Sunday, Mr McGowan described the assault and following unrest as shocking, and said the detainees, mostly aged under 18, would now face charges.

“I know there are a lot of people out there who make excuses and don’t think they should be in custody. I disagree with them. If you commit those sorts of offences you’ve got to face the consequences.

“And the consequences are, if you keep doing it, you go into some sort of custody,” he said.

It’s understood the riot began in the afternoon in unit 18 of the centre, the youth detention wing of the facility located south of Perth.

By Kathryn Magann in Sydney