Man arrested over post office robbery

A man has been arrested after a robbery at a post office in the Adelaide Hills.

The man threatened staff at the Nairne store with a pair of scissors and made off with cash not long before 1pm on Wednesday, police say.

He fled in a car but was forced to abandon the vehicle after crashing into a tree.

Just before 4pm, a member of the public noticed a man matching a description released by police and contacted triple-0.

The man is currently being interviewed by police.