Search teams have gone to the area where the skeletal remains of a child who "has clearly been murdered" were found by a passing motorist near the Karoonda Highway in South Australia's Murray Mallee.

Police made their assessment after a member of the public reporting finding the bones on Wednesday morning.

Detective Superintendent Des Bray said the motorist was driving along the highway when their attention was "drawn to something on the side of the road".

"They stopped, had a look behind some bushes, and found what we now know to be the skeleton of a young child," he said.

A suitcase and scattered clothes were found nearby.

A forensic investigation is being made and police are treating the discovery as a major crime.

About 20 State Emergency Service volunteers arrived at the scene on Thursday morning to assist police with a detailed search.

Police Commissioner Gary Burns said police would be undertaking investigations with people who regularly travelled the road or lived on properties in the vicinity.

Superintendent Des Bray speaks to media about the discovery of a child's remains in SA's Murray Mallee. ( ABC News )

Superintendent Bray said police were not able to say how long the child's remains had been there or the gender, "but it's clear to us it's foul play".

"We have the skeletal remains of a young child, someone who I would suggest has clearly been murdered," he said.

The bones were found about two kilometres west of Wynarka, about 130 kilometres east of Adelaide.

There is a two-metre verge aside the Karoonda Highway bitumen and the remains were found immediately behind a bush near the verge.

"Somebody must know somebody where a child has disappeared in suspicious circumstances," Superintendent Bray said.

"So we would encourage people to have a think about family, friends, acquaintances, people who live near them, perhaps somebody who has had concerns about children who live nearby and how they might be treated, and all of sudden a child's gone missing.

"It's impossible for someone not to know."

Police are checking interstate missing persons databases because there is no-one on the South Australian database who is thought to match the discovery.