More than 75 community organisations have called on the West Australian government to enact immediate reform to the youth justice system in response to the government's plan to shift 20 children, the youngest of whom is 14, to a maximum security adult prison.

The groups released an open letter to the government on Friday in opposition to the decision to shift minors, currently in Banksia Hill detention centre, to a standalone temporary unit at Casuarina Prison.

Advocates, including Social Reinvestment WA and the Commissioner for Children and Young People, visited the facility last week and said the environment was not suitable for children.

Social Reinvestment WA said a previous gazettal of Banksia Hill Detention Centre detainees at Hakea Prison in 2013 resulted in children requiring "long-term psychological support, including support for post-traumatic stress disorder".

The open letter calls on the WA government abandon the Casuarina transfer plan and provide alternative solutions to confront the immediate crisis in the youth justice system.

The letter focusses on investing in community-based supports, providing comprehensive trauma-informed care for the young people, and systemic reform to prevent children from entering detention in the first place.

Social Reinvestment WA co-chairperson Glenda Kickett said children in Banksia Hill have unmet needs, experienced major disadvantage, and have unaddressed trauma.

"We know our system should be focused on identifying these needs earlier and providing children the supports they desperately need â€" not punishing them for their circumstances," she said.

"Children need support and care to thrive, especially vulnerable children who are already in distress - adult prison is not the answer.

"As Aboriginal people we know our children and young people should be home in their communities with their family, and culture is their strength and security, not locked up in prisons."

Ms Kickett said the detention of young people on remand must end and the age of criminal responsibility must be raised to at least 14, combined with investment in caring for children in their own community.

Social Reinvestment WA lived experience ambassador Joanne Ugle said Banksia Hill was the root of the problem.

"The kids in Banksia need to hear hope," she said.

"We need to raise our voices for our kids."

Wungening Aboriginal Corporation chief executive Daniel Morrison said government failures to invest in the alternatives had led to the transfer of children to an adult prison.

"We need a holistic strategy for youth justice that prioritises prevention, invests in community-based programs that provide support, and creates alternatives to detention such as on-country camps and alcohol and other drug programs," he said.

Last week a spokesperson for the WA Department of Justice said the transfer to Casuarina Prison was necessary to relocate the cohort of about 20 detainees to "a safer and more secure place".

"The temporary youth detention centre will be managed by Youth Custodial Officers and other Banksia Hill and Youth Justice staff," they said.

"All the same services offered at Banksia Hill including medical, mental health, education and other support programs will also be delivered at the newly gazetted facility. They will also have access to secure recreational areas."

The spokesperson said family members, lawyers and case managers will be able to visit the detainees as they do at Banksia Hill.

"The temporary centre will be separate from the rest of Casuarina Prison and detainees accommodated there will have no contact with adult prisoners."

The open letter calls on the WA government to:

Take immediate action to not send these children to adult prison.

Develop and implement tailored trauma informed treatment and rehabilitation plans for these young people, based on comprehensive assessments of their needs.

Provide an adequate Model of Care in Youth Detention, building pathways out.

Immediately invest in community-based alternatives to detention and move children aged 10 to 13 out of Banksia Hill Detention Centre.

Reform legislation to prioritise diversion and prevention, including Raising the Age of Criminal Responsibility from 10 to 14 years and abolishing mandatory sentencing.

Develop a cross-government vision and strategy to fix our broken youth justice system.

Identify the communities in most urgent need of youth justice action, and resource place-based justice reinvestment initiatives to address the root causes of offending.