Detectives investigating two incidents in Chorley have launched a CCTV appeal for information.
Around 5.35am on April 14, a man entered Premier Newsagents in Pall Mall carrying a knife.
The offender approached a staff member, a 57-year-old man from Chorley, urging him to hand over cash from the till.
The victim refused, fighting off the attacker. The suspect made off from the scene empty-handed.
Around 11.20am on the same day, a man entered Collingwood Convenience Store in Collingwood Road carrying a knife.
He threatened a staff member, a 50-year-old woman from Chorley, before removing a quantity of cash and coins from the till and making off from the scene.
The offender in both incidents is described as male, wearing a black jacket over a grey hooded top with a snood covering his face. He also had black pants, black footwear and black gloves.
Detectives believe both crimes are linked and are appealing for information.
Det Con Phil Hampson, of Skelmersdale CID, said: “We are appealing for information following a robbery and an attempted robbery in Chorley.
“On both occasions a man has entered the store brandishing a knife before threatening a shopkeeper.
“Both staff members have been left shaken by their ordeals and we need to find the person responsible.
“We are urging anyone who recognises the offender to contact us immediately.”
Anyone with information can contact police on 101 quoting crime reference SC1702837 for the first offence and SC1702849 for the second incident.
Alternatively Crimestoppers – the independent charity – can be contacted anonymously on 0800 555 111 or online at Crimestoppers-uk.org.