The culprits tried to steal from South Cliff Post Office on Filey Road in broad daylight at around 3.40pm.
A spokesperson for Post Office confirmed there was an attempted armed robbery at its South Cliff store.
"The people who run our Post Office branches provide important services to local communities," he added.
"This type of crime is very traumatic for the retailer and we will be supporting the police in their efforts.
"Post Office would urge anyone with information to contact the police or Crimestoppers anonymously on 0800 555111.”
Anyone with information about the attempted robbery bid can call police via 101.