Police in Perth say they are treating the discovery of a man's body in the Supreme Court Gardens as suspicious.

A member of the public found the body just after 8:00 am in a garden bed off St Georges Terrace.

Inspector George McIntosh says police are trying to establish the cause of death.

"The circumstances surrounding that person passing away is unknown at this particular point in time and members of the Major Crime Squad are going to investigate those circumstances," he said.

"As with any death it's treated as suspicious until we can prove otherwise, so at this point in time Major Crime are looking into the matter."