Fulwood residents were awoken to the sound of an explosion late on Wednesday.
A raid on a Post Office cash machine saw a heavy police presence in Garstang Road.
The Sharoe Green Post Office has been targeted by cash point raiders around 11.40pm.
Police closed off the road at the junction with Brookside Avenue.
One woman, who lives nearby, told Blog Preston: “I grew up in Northern Ireland and it sounded like explosives.
“There was a massive boom and it shook our whole house.
“There were loads of police on the scene and traffic was stopped.”
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Preston Police have now launched an appeal for witnesses.