Australian police said a child whose skeletal remains were found inside a suitcase dumped on the side of a highway near Adelaide was likely murdered up to eight years ago.

Authorities in South Australia asked anyone with information to come forward as they are struggling to identify the body.

Detective Superintendent Des Bray said there are reasons to believe the victim was a little girl with fair hair aged between two and four.

"While the forensic analysis has not yet provided a conclusive result regarding this child's gender, we are reasonably confident at this time that these are the remains of a girl who had fair hair and was 90-95cm tall," he said.

"For reasons I'm not going to disclose we are confident that this child was murdered."

The remains were found by a passer-by in the bushes off a road near the small town of Wynarka, some 130km (80 miles) east of Adelaide, on 15 July.

Police said the child was probably killed elsewhere and then brought to the location inside a black suitcase which has since been turned grey by sun and weather exposure.

Inside the case were girl's clothing including a black tutu and a purple top dating back to 2007, leading detectives to believe she was killed around that time.

"At this time 24 children have been nominated as potential victims, but have been ruled out by investigators who have determined that they are alive and not requiring any further police attention," Bray told a press conference on 24 July.

"We want people to think back into the past, back to 2007 and the years in between, think about little girls like this -- who lived near them, played near them, they may be related to -- and think about where those children are now".

Investigators said before the discovery was reported someone had dug into the suitcase, tipping some of its contents outside.

Police said they want to talk to a Caucasian man, aged about 60 who was seen near the scene with a suitcase six to eight weeks ago.

Authorities asked anyone with information related to the case to contact Crime Stoppers on 1800 333 000 or report online.