Police are now appealing for information following the incident.
Police have released CCTV images of the moment a man robbed a St Neots shop at knifepoint.
Officers were called at just after 10.30pm on Tuesday (February 18) to reports of a man, armed with a knife, entering Tesco petrol station in Barford Road with his face covered.
Cashiers told officers the man approached them and demanded cash.
He fled the scene after staff handed over £790.
Detective Inspector Dave Savill said: "This was an extremely distressing incident for those working at the time.
"I'm urging anybody who recognises the clothing the man is wearing, or anybody who was in the area at the time and saw something suspicious, to contact us as a matter of urgency."
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Anyone who recognises the man or has any information regarding the incident should call police on 101 quoting 35/12528/20 or contact Crimestoppers, anonymously, on 0800 555111 or via www.crimestoppers-uk.org.