Eighteen-year-old Eddie Harris had gone for a late-night drive with a friend when they were approached by four men in two cars at Black Hill’s lookout about 3.45am on Monday.

Mr Harris said one of the offenders suddenly leapt out of his car and fired a gun into the air before aiming it directly at him, demanding he hand over the keys to his new silver Ford Falcon FG.

“I had a gun pointed at me … I was shocked, I didn’t know what to do,” Mr Harris said.

“He was wearing a balaclava and holding what looked like a shotgun.”

The gunman then snatched Mr Harris’ keys and sped off in his silver Ford Falcon, with his accomplices following in the other two cars.

The four men were aged between their mid-20s to early 30s, according to Mr Harris.

The incident was the subject of an ongoing investigation by Victoria Police’s armed crime squad detectives, who were based at Melbourne’s Spencer Street station.

The probe comes as Assistant Commissioner Robert Hill announced on Friday tracking devices would be installed in Melbourne cars in a trial aimed at reducing car theft and deterring thieves.

GPS devices will be fitted into at least 1000 cars from September as part of a 12-month trial.

Police eventually want to have the devices fitted in all Victorian cars.

"Vehicles can be tracked anywhere across the state, the nation and the globe if required," Assistant Commissioner Hill told radio station 3AW on Friday.

Two other alleged carjackings at Lake Wendouree and Delacombe had sent shock waves through Ballarat just last month.

The Victorian Government introduced two new offences including carjacking and aggravated carjacking back in December.

Carjacking carries a maximum penalty of 15 years and those convicted of aggravated carjacking would face a maximum penalty of 25 years. A statutory minimum non-parole period of three years also applies to aggravated carjacking. 

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report online.