Lancashire Constabulary said officers were called to the branch at 10.37am on Tuesday (21 September) following reports of a robbery.
Police said a man is alleged to have passed a note to a member of staff, in which he claimed to have a gun and demanded money. No weapon was seen and the man left with a large quantity of cash, said the force.
Officers then attended the same store on Wednesday (22 September) where an individual reportedly brandished a knife, threatened staff, and demanded money, again leaving with a large quantity of cash.
A spokesperson for Lancashire Constabulary said: "We realise these incidents will cause a great deal of a concern to members of the public and there continue to be increased patrols in the area."
Anyone with information is asked to call Lancashire Constabulary on 101 quoting log 0698 of 22 September 2021.
