A spate of cash point fraud is thought to have taken place throughout Hertfordshire.

Police officers in the county are warning residents to "be vigilant" if they use ATMs in the county.

Several thefts are reported to have taken place as a result of tampering.

On one occasion, a victim was guarding the ATM she was using while on the phone to the bank, according to social media reports. Cash was taken from her account at an ATM elsewhere while the card was still using her machine.

Detective Sergeant Mark Fava, of Hertfordshire Constabulary, said: "It appears that these thefts are being achieved by a discreet device being placed over the card slot of the machine, which scans the card details, transmits the data to the criminal and then blocks the card from being returned.

"The best way to avoid this happening to you is to cancel or suspend your bank card if it is retained by an ATM.

"If you have a banking app on your phone you may be able to freeze your card temporarily until you can establish what has happened.

"Alternatively, you may need to call your bank to cancel or suspend the card until it has been recovered."

A police spokesperson said ATM users should shield their PINs and examine the machines before they take cash out.

If the machine looks like it has been tampered with, ATM users should phone their bank.

If the machine "swallows" the card or does not return cash, ATM users are being asked to phone the police's non-emergency line on 101.