Man on the run after SA knife carjacking

A man has threatened a couple with a knife and stolen their vehicle as they sat in a car park in Adelaide's north.

Police say a man and woman were sitting in the Para Hills car park when the carjacker approached them early on Thursday morning.

The robber remains on the run and has been described as being Caucasian, with black hair and aged in his late 20s or early 30s.