WA's police commissioner says up to 24 nurses could be given special powers to help police who encounter suspects with a mental illness.

Nurses given limited police powers as part of proposed mental health teams would only be called out for crisis intervention, the West Australian police commissioner says.

The state government is proposing the nurses be given special powers, like being able stop and search someone, to help police who encounter offenders with a mental illness.

Karl O'Callaghan said that there could be up 24 nurses with the limited powers across Perth's four policing districts.

"You just can't train police to deal with all the mental health issues you might come across," he told ABC radio on Monday.

Mental health minister Helen Morton said on Sunday that the teams would ensure people experiencing a sudden or escalation of mental illness would be treated from a health perspective, rather than a justice one.

But opposition police spokeswoman Michelle Roberts said the plan had been done "on the hop", with the minister not even knowing how the powers would be brought about.

The government has not decided whether it will legislate the changes or ask the commissioner to give the nurses special constable powers as he has done for Transperth guards.

Ms Roberts said she hoped the plan wasn't a ploy to cover up the fact the government had failed to deliver on its promise to employ more police.