A man wearing a crash helmet robbed a newsagents with a gun.
The man entered Maxted News and Food in Worthing Road, Rustington, carrying a firearm and demanding money from the till at 5.20pm yesterday evening.
He made off on foot with cash.
Police are investigating and the man is described as 5 ft 10in to 6ft and in addition to the crash helmet was wearing a blue hooded top.
Detective Sergeant Colin O'Hare, of West Sussex CID, said: "Incidents like this are rare, and while staff were shaken no one was injured during this incident.
"Anyone who saw what happened or noticed anything suspicious in the area is asked to get in touch as soon as possible. They should phone Sussex Police on 101 or email firstname.lastname@example.org, quoting serial 1213 of 14/5."
Alternatively, anyone with information can contact the independent charity Crimestoppers free and anonymously on 0800 555111.