Police sealed off the Hilperton Marsh Post Office on Tuesday, September 24.
The Post Office at the Central Convenience Store on Wyke Road was closed and a police officer stood guard outside on the forecourt.
Police later sent a Forensic Services Crime Investigation Unit to the scene.
A Wiltshire Times witness at the scene was told by officers that the premises had been "burgled".
Despite this the staff posted a notice in the window saying: “Store closed due to clear up due flooding”.
A Wiltshire Police spokesperson said: "We are investigating a burglary at the Hilperton Post Office which occurred between 8pm last night (23/9) and 6am this morning (24/9).
"Enquiries are currently ongoing to ascertain exactly what has been stolen, if anything.
"Anyone who saw or heard anything suspicious at the store in Wyke Road should call 101 and quote log number 69 of September 24."
A reporter also called the shop but no-one has since answered.
Last week a masked gang dressed in dark clothing and balaclavas raided the Budgens convenience store at the BP filling station on the West Ashton Road.
The main items being stolen are cigarettes, tobacco, vapes and alcohol.
It is not yet known if anything was taken following this incident.
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