An armed robber waved a knife at a female shop worker before escaping with a bundle of cash, police said.
The man, whose description has not yet been released, walked into the Co-op in Lytham Road, Freckleton, at around 9.50pm yesterday.
He threatened the woman before escaping with cash notes out the till, a spokeswoman for Lancashire Police said.
The Co-op did not say whether the staff member was hurt, or how much money was taken.
In a statement, a spokesman said: "The safety of our colleagues and customers is of paramount importance and the Co-op takes retail crime very seriously.
"We are implementing a number of measures to deter both criminal activity and aid convictions.
"The police are investigating, and we appeal for anyone with information to come forward.
"The store has now re-opened to serve the community."
Last June, three men in balaclavas burst into the nearby Post Office, also in Lytham Road, and attacked a female member of staff, 55, who suffered minor injuries.
After stealing hundreds of pounds in cash and cigarettes, they escaped in a black SUV-type car that was seen driving off towards Preston.
The robbery happened at around 11.30am on Friday, June 23, and the men were dressed in black, with orange and black gloves.
One witness said: “I think they have beaten somebody up and gone to the owner with some sort of arms.
“There was about 10 police cars here.”
Detectives said the female worker was treated by paramedics at the scene after being manhandled.
Sgt David Priest, of Blackpool Police, said at the time: “This was a nasty incident which has left a member of staff extremely shaken. We are determined to trace those responsible.”
More to follow