The five man gang, who were armed with a hatchet, a bat and a knife, got away with an undisclosed sum of money.
The gang threatened staff and customers before making their getaway.
The gang also crashed into a number of cars as they made their getaway around 11am this morning.
The gang travelled in the wrong direction before doing a u-turn on the Main Street and driving in the direction of Derry.
Nobody was hurt during the raid but staff and customers were left shocked by their ordeal.
This day last year another gang, armed with a handgun, took just 18 seconds to rob the post office.
Local Fianna Fail county council Paul Canning said things have got so bad that businesses almost have a bag of money ready for would-be robbers.
“That is how bad it has got and it’s no laughing matter.
“How many post offices, shops and other businesses have to be raided before something is done,” he said.
Cllr Canning has been highlighting the amount of criminality in the area and he puts much of it down to the lack of Garda manpower.
“You can pick 12 roads from Donegal back into Derry and none of them are manned by Gardai.
“It’s easy pickings and they can take their pick of their getaway routs.
“I will continue to highlight the lack of Garda manpower and vehicles along the border areas from Carrigans to Muff,” he said.
Cllr Canning revealed he now has a meeting with Acting Garda Chief Superintendent Jim Sheridan to discuss the rise in crime in the area.