Police are appealing for help to identify a man who tried to snatch a child from Kings Park on Tuesday.

A four-year-old boy was playing near family at Synergy Park on May Drive in Kings Park when a stranger picked him up and started to walk away.

The alleged abductor put the child down after being challenged by an adult who witnessed the incident and walked towards an access road where several vehicles were parked.

The wanted man, who was believed to be aged in his 30s, has fair skin, is about 177cms tall with a slim build and short light brown hair.

He was wearing a blue loose fitting polo T-shirt, baggy knee-length shorts and a white baseball cap.

Detectives would like to speak to anyone who took photographs or video in the park between 1pm and 5pm and who may have captured an image of the man.

They also want speak to the driver of a black Ford Territory which was parked on the side of the road next to a toilet block.

Anyone with information can call Crime Stoppers on 1800 333 000 or make a report online at www.crimestopperswa.com.au