A would-be carjacker is on the run after being fought off by a 48-year-old man armed with a jar of instant coffee.

The incident occurred at a Nepean Highway service station at 9.40pm on Tuesday.

Watch the video above

The victim, Jason, was at his local Frankston service station grabbing coffee and cigarettes when he was confronted by an unknown man.

The man, armed with a handgun, demanded the victim's Mercedes keys - but he refused.

"I sort of stepped back and said, 'No, you're not getting my keys'" he told 7NEWS.

Nescafe Blend 43

His weapon of choice? Nescafe Blend 43.

"As I kicked him, he struck me on the top of the head with the firearm."

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The offender then struck the man to the forehead before stealing cigarettes and fleeing in a waiting vehicle.

The vehicle is described as a brown or maroon VT Commodore with no registration plates.

On reflection, the Frankston South man, who sustained a minor injury, says "I think most people probably should hand the keys over, but I'm sort of not one of those people".

Police have released images of the man in question, he's described as caucasian, 183cm and in his 20s.

It's the latest in a number of attempted carjackings in the state.