WA premier says youth detention centre riot 'terrorism'

Most inmates involved a major disturbance involving dozens of juveniles at Perth's Banksia Hill Detention Centre have surrendered, as authorities regain control of the troubled facility.

Premier Mark McGowan said the riot was "utterly unacceptable" and the youths' behaviour was "a form of terrorism".

A number of detainees breached their cells about 8.30pm on Tuesday and gained access to the grounds of the facility before climbing onto the roof.

They lit fires in several accommodation blocks and caused extensive damage to the troubled facility, where about 90 youths are detained.

Mr McGowan said he was not sure how many detainees remained on the "loose" but most had now surrendered to authorities.

"Obviously, it's total and utterly unacceptable," he told reporters on Wednesday.

"It's a form of terrorism they are engaged in and they are behaving in an appalling way, with no respect for anyone."

The premier said the riot started when an inmate escaped from his cell and threatened a custodial officer with a brick.

"She retreated to a safe place (and) as she did, a key that she had got lodged in a door as she tried to escape from this juvenile that was threatening her with a brick," he said.

"The detainee took the key and then unlocked a range of accommodation units and cells around Banksia Hill."

Mr McGowan said more than half of the centre's inmates left their units and cells once they were unlocked.

"The authorities then declared there was an emergency ... (and) scrambled various resources to try and contain the situation," he said.

This included the special operations group and firefighters, who were supported by a large police contingent including a helicopter and dog unit.

"A range of (detainees) then tried to stop the fire trucks from getting access to put out fires," Mr McGowan said.

Others threw debris at staff and authorities from the roof and rammed a motorised buggy used in the centre into gates and doors. 

"Fortunately none of the staff were injured. I am advised no one has been injured," he said.

"A range of them (also) started tying sheets together to try and climb the fences but fortunately the accommodation is secure and there was no prospect of them escaping."

"The general public has got nothing to fear."

Mr McGowan said initial reports some detainees had been injured by other detainees are likely incorrect.

He also said laws would be drafted and passed to transfer six detainees, who are over 18 and involved in the disturbance, to an adult correctional facility.

The Department of Justice earlier said significant damage had been caused across the site.

Banksia Hill is a juvenile facility for offenders aged 10 to 17.

A guard suffered a suspected fractured skull after being hit by objects allegedly thrown by detainees at Banksia Hill in February.

Seven climbed fences and rooftops after absconding from activities outside their cells, and allegedly ripped pieces of masonry and metal off the facilities and threw them at youth custodial officers, four of whom were injured.