Melbourne man carjacked at gunpoint

A man who allegedly had a pistol held to his head during a Melbourne car-jacking thought the gun was fake till he heard it being cocked.

The 21-year-old man was on his way to get milk in St Albans, in Melbourne's west, about 7.45pm on Monday when another man confronted his car.

"Next minute he pulled a nine millimetre, (put it) to his head, and said `I want the car`," the victim's father, Peter, told 3AW.

"My son thought it was still a joke, a plastic (gun), but then when he cocked it my son thought it was serious, he handed him the keys."

Highway patrol officers spotted an allegedly stolen car just after 8pm and police later arrested a 21-year-old St Albans man in Broadmeadows.

The man is due to appear at Melbourne Magistrates' Court on Tuesday charged with armed robbery.