Detectives are searching for two knife-wielding men who threatened two female shop assistants with kitchen knives and ran off with a cash till tray.
The incident happened at 1750 BST on Wednesday at a Spar store in Swansea city centre.
"This was an extremely frightening experience for these two ladies," said Acting Det Insp John Bainbridge.
South Wales Police are appealing for witnesses.
The two male suspects walked into the store at the junction of St Helen's Avenue and Francis Street armed with what appeared to be black-handled kitchen knives and demanded cash, said police.
When the till was opened, one of the men took the plastic internal cash tray and both ran out of the shop.
They were then seen to run up Francis Street and in the direction of King Edward Road.
The suspects were described as being white and 5ft 11in and 5ft 4in tall respectively.
Both were said to be wearing light or cream scarves, to hide their faces, and gloves.
Acting Det Insp Bainbridge added: "This incident happened during the early part of the evening, in a busy residential area when there would have been a lot of people around.
"These men would have stood out as one of them was carrying a cash tray.
"We believe that there a number of people both inside and outside the shop at the time of the incident, who have not yet come forward."
Anyone with information can contact the CID in Swansea on 01792 450618 or Crimestoppers on 0800 555 111.