The West Australian Government plans to introduce a specialist court to deal with offenders suffering from mental illness.

WA Mental Health Minister Helen Morton says the state government will draw on the experience of other jurisdictions for its planned mental health court.

Under the proposal, offenders with mental illness will be assessed prior to appearing before a dedicated magistrate and the nature of their condition will be taken into account when sentencing.

The 2-year trial program is tipped to cater for up to 300 people a year and cost $5-million.

Similar courts have been implemented across Australia, and Minister Helen Morton says those programs have played an important role in the development of the government's proposal.

"In developing this new program the Mental Health Commission and the Department of the Attorney General have taken on board the results from other jurisdictions in Australia and other jurisdictions overseas and all of those results have been overwhelmingly positive," she said.

The West Australian Greens have welcomed the Government's plans, describing the decision as heartening.

Greens member Alison Xamon says if the pilot program is successful it will need to be expanded considerably.

But she says more diversionary programs are needed, particularly in regional areas.

"These courts are only successful when you ensure that the follow-up services are there," she said.

Participation in the court will be voluntary and a range of factors including the nature of offending, the particular mental illness, risks to community safety and victims will be taken into account in determining an offender's suitability for the court.

WA Mental Health Minister Helen Morton will also announce $1.7 million for mental health experts at the Perth Children's Court for a pilot early intervention program, saying it is essential to identify young offenders early and identify appropriate services.

"Too often, these people are inappropriately and expensively caught up in the criminal justice system when they should be receiving effective mental health care," she said.

"Traditional methods of sentencing have little impact on people with mental illness and often fail to address the cause of the offending."