The incident happened at the shop on Barnsley Road in South Elmsall after 4am this morning, Friday, December 21.
Police were called to reports of a cash machine being vandalised.
Two males were seen damaging the ATM but fled as soon as the alarm sounded and drove from the scene in a black car.
Nothing was taken from the machine.
Police are conducting enquiries in the area, including examining CCTV.
Anyone who witnessed the incident or has any information is asked to contact the police via 101 quoting crime reference number 13180638030 or information can be passed to Crimestoppers anonymously on 0800 555 111.
The Post Office remains closed this morning with the owners saying they will re-open once the police have finished their investigation.