Police are investigating after a convenience store was robbed at South Townsville this afternoon.

Around 1.30pm a man entered the Boundary Street business and jumped over the counter. He attempted to open the cash register without success before jumping back over the counter. The man then produced a knife, threatened the attendant and demanded the register be opened.

After the female attendant opened the register the man took cash from the drawer before running from the store. He was last seen on Nelson Street.

The attendant, a 72-year-old woman, was not physically harmed.

The man is described as Caucasian, aged possibly mid to late twenties and was wearing black and light coloured two tone jacket, black trousers and with a black balaclava.