A Scots teenager has admitted murdering a family-of-three in South Australia.

Jason Downie, who is originally from Ayrshire, stabbed 16-year-old Chantelle Rowe and her parents Andrew and Rose at their home in Kapunda, near Adelaide.

Downie, 19, pled guilty to the murders over a video link to the Elizabeth Magistrates' Court.

He had also been accused of one count of rape, but that was withdrawn due to lack of evidence.

The teenager handed himself in to authorities nine days after committing the crimes in November 2010.

Downie will be sentenced in December at the Supreme Court.