According to Sussex Police, at 9.55pm on Monday, November 23 the man entered the Co-operative in Queen Street, Arundel, threatened staff with what appeared to be a handgun, and stole about £4000 in cash. There were no shots or injuries reported, police said.
The suspect was described by police as in his 30s, wearing a black mask, a hat, coat and purple or black trainers.
A spokesman for the force said: “Police would like to hear from anyone who witnessed the incident or noticed a man matching this description in the area at this time. It is believed a woman may have entered the shop during the incident and police are urging this person to make contact with them.”
As a result of the incident, officers will be conducting high visibility patrols in the area and the search for the suspect continues.
Anyone who saw what happened or who has any other information can contact Sussex Police online or by calling 101, quoting serial 1450 of 23/11. They can also contact the independent charity Crimestoppers anonymously on 0800 555 111.