The Western Australian Government has announced plans to establish an online register to allow members of the public to identify, report and seek information about serious sex offenders.

Western Australian authorities already monitor the movements of such offenders, but the new legislation would allow the public to track the names and images of serious or repeat offenders in their suburb through a police website.

Police Minister Rob Johnson says parents or guardians would also be able to lodge an online inquiry with police if they suspect a person in contact with their child is a reportable sex offender.

"They will be furnished with a photograph of that sex offender that lives within those postcode areas and that means that the parents can then keep a watchout for that person and make sure that their children make no contact with them," he said.

The Minister says the legislation, to be introduced into the State Parliament on Tuesday, is unique in Australia.

Law Society of WA president Hylton Quail, has described the proposal as a "retrograde and dangerous step" that could encourage vigilante behaviour.

But Mr Johnson has dismissed the suggestions.

"We believe that the public will act responsibly and appreciate the fact that there will be some information available that is purely designed to protect the safety and sexual safety of children in the community," he said.

He says the register does not represent an admission that sex offenders are not being adequately monitored by the relevant authorities.

"Where those offenders that do not report as they should do under their orders, we want the public to be able to identify them and where they are," he said.

The State Opposition says it is unlikely to support the Government's plans.

Labor's Police spokeswoman, Margaret Quirk, says she has serious doubts about its merits.

"It is a very dangerous and populous move to more broadly publicise the whereabouts of these people," she said.