An armed robber held up a fast food restaurant at gunpoint and demanded they open the safe - making off with a "substantial" amount of cash.
The gunman entered Uncle Sams fast food restaurant on Crabtree Lane, Lancing, and pointed a black handgun at an 18-year-old female member of staff, ordering her to open the safe.
The incident occured at around 10.15pm on Saturday.
The suspect is described as white, slim and not tall, and he spoke English. He was wearing dark clothing with something covering the bottom half of his face, and he had a hood covering his head.
He was wearing gloves and carrying a black self loading type handgun with a red foresight.
Police forensic officers examined the scene and CCTV is being reviewed.
Detective Sergeant Colin O'Hare said "This is a very serious incident. The staff were unhurt but very shaken by the experience and to point the gun at the woman and forcing her to open the safe shows great callousness. This man needs to be caught and brought to justice as soon as possible.
"If you were in the area and saw this man, or if you have any other information, please contact us right away. You can call us on 101 quoting serial 1565 of 31/5, or call the independent charity Crimestoppers on 0800 555 111."