While carjacking is a crime in NSW, offenders in Victoria are typically charged with multiple offences, such as theft of a motor vehicle and armed robbery.

The latest incident in Melbourne's south-east happened when a 23-year-old driving a 2015 Audi was attacked at the intersection of Wattletree and Glenferrie roads at 2.15am on Wednesday.

He was bumped from behind by a BMW, which caused him to pull over. He was then assaulted with a crowbar and his keys were stolen by a passenger in the BMW, which had parked in front of him.

A day before, a similar method was used to steal a Mercedes at the traffic lights at the intersection of Waverley and Belgrave roads. A 16-year-old was charged and police do not believe the two incidents are linked.

"We think it's just a copycat offence," Inspector Mick Daley said.

The crime is becoming increasingly common in Melbourne and it's difficult to tell if authorities are tracking it accurately. Carjacking doesn't exist as an offence in Victoria, but it can be tracked by pairing the offence of car theft with others such as robbery or assault.

Crime Statistics Agency figures released last week showed the number of crimes that fit this matrix has almost doubled, from 183 to 362, in the past five years.

Attorney-General Martin Pakula said the state government was "looking very closely" at amending the Crimes Act to introduce carjacking as a stand-alone crime, which NSW did in 2001.

This would "send a stronger message, but also make it easier for Victoria Police to charge with that specific offence", Mr Pakula told radio station 3AW on Wednesday.

As well as simplifying the jobs of police and the courts, Mr Pakula said, a specific offence with strong penalties would act at a deterrent.

National Motor Vehicle Theft Reduction Council executive director Ray Carroll said accurate data would be the only real benefit of introducing a stand-alone offence.

He said the charges against someone who commits a carjacking could include armed robbery, which attracts a maximum sentence of 25 years already.

"It's what happens to them [at court] after they're arrested. You see cases, particularly in the Children's Court, where they're already on five sets of bail and they're giving it to them again," Mr Carroll said.

Police Association secretary Ron Iddles backed the introduction of a carjacking offence.

"It's more than a theft of a motor car and it's regularly done in violent circumstances," he said.

But more effective, he said, would be an increased police presence on the streets and in stations.

"Will it stop it completely? No. But it will act as a deterrent," he said.

Carjacking is not a new phenomena. The United States experienced a surge in carjacking in the early 1990s, and Britain saw a similar trend from the late 1990s, where advances in car security meant thieves had to get their hands on the key instead of hotwiring the car. There, criminals also used the "bumping" methodology (hitting a car from behind while slowing down at traffic lights).

Mr Carroll said the reasons behind a carjacking vary. He said mostly cars are stolen to commit other crimes or for the thrill, but there are also organised rackets that sell the car for parts that are then shipped to Asia and the Middle East.

"There is a strong, legitimate car parts market for export out of Australia. So where there's a legitimate market, there's an illegal one," he said.

He said high-end cars, like Audi, BMW and Mercedes, could be sold for parts for between $1500 to $3000.

Most of these cars though, he said, are "thrashed" and dumped.