Police are investigating an aggravated robbery that occurred last night at Salisbury Downs.

At about 10pm a male armed with a knife entered a petrol station on Winzor Street, threatened staff and fled on foot with an amount of cash.

He was last seen in a reserve at the rear of the petrol station.

Police, including members of the Dog Operations Unit searched the area but were unable to locate the male.

The suspect is a man of Caucasian appearance, aged in his 30’s, about 175cm tall, slender build, with two days growth of facial hair and was carrying a green shopping bag.

He was wearing a black jumper, black pants and a black beanie.

Police urge any member of the public with information in relation to this incident to contact BankSA Crime Stoppers on 1800 333 000 or on line at www.sa.crimestoppers.com.au

CCTV image of the suspect appears below.