Two robbers threatened shop staff before making off with cash.
The Co-op shop on West End Road, Haydock, was targeted at about 5.20pm last Monday (April 28).
Police say two men entered the store and threatened staff - forcing them to hand over money. The two offenders then made off with a quantity of cash in the direction of Park Street.
Nobody was hurt during the incident.
Detectives are now speaking to witnesses and CCTV from the area is being checked in an effort to identify those responsible.
One of the offenders is believed to be about 20 years of ge and was wearing a dark hooded top and grey shorts.
The other offender was wearing a grey or blue coat. Both had Liverpool accents.
DI Martin Earl, of St Helens CID, said: “We are determined to find the people responsible for this incident. A number of staff have been left really upset following their ordeal and I know the community will join with me in wanting to see the people who did this brought to justice.
“This is a busy area and I would appeal for anyone who might have seen two people acting suspiciously at around the time of the incident to call police.
“You might have some very important information that could help our inquiries.”
Anyone with information can call St Helens CID on 0151 777 6812 or Crimestoppers, in confidence, on 0800 555 111.