South Australian police say the discovery of human remains north of Adelaide is now a murder investigation.

The remains were found in a shallow grave near the side of a road at Long Plains on Friday afternoon by a land owner carrying out earth moving.

Detective Inspector Mark Trenwith says it is likely the body has been there for less than five years.

"A forensic anthropologist attended at the scene and she's conducted a preliminary examination of the remains, but at this stage we can't confirm the age, identity, ethnicity or sex of the remains," he said.

Inspector Trenwith says the body could be linked to an unsolved murder investigation.

"As part of our initial investigation we're reviewing missing person's files and also previous murder files where bodies have not been located," he said.

"There have been a number of murder investigations where bodies have not been recovered. Some matters have even been through the courts.

"We'll be checking dental records and using DNA technology in an effort to identify this body as quickly as we can.

"It may well be that someone remembers seeing someone out in that area acting suspiciously over the last few years.

"It may well be that someone out there has heard rumours about someone coming to grief and being buried out in that area. So we'll be interested in speaking to anyone who has information."