Police say petrol thieves are either siphoning fuel from cars or stealing numberplates and using them in petrol station drive-offs, in which they speed away without paying.

Senior Constable Justin Stanton of the Casey crime investigation unit said: "In Casey it has been a concern for the past three years, with the number of incidents on the increase.''

He said the Narre Warren, Berwick, Cranbourne, Hallam and Merinda Park railway station car parks and car parks at the Cranbourne, Fountain Gate and Endeavour Hills shopping centres were increasingly being used as hunting grounds by petrol thieves.

The thieves were intent on stealing vehicles' GPS units, numberplates and, in some instances, petrol.

He said people targeting vehicles for petrol concentrated on railway station car parks because they knew there was a good chance they would not be disturbed.

"There have been instances in residential areas, usually at night, where petrol has been siphoned from vehicles parked unattended in the street.

"Many people don't report it because they are not aware of it.

"These people can go around to several cars with a jerry can ... many people would not notice five litres being taken from their tank.''

The concerning trend was raised at a Casey Council meeting last Tuesday by Cr Lorraine Wreford, who successfully moved that the council ask Public Transport Minister Lynne Kosky for urgent security upgrades at Casey railway station car parks.

The council also resolved to initiate talks with local police about the possibility of police or security patrols of the car parks.

Cr Wreford said she was concerned about the plight of a resident whose car had petrol and its numberplates stolen in three incidents when parked at the Berwick railway station.

"Given the price of fuel being what it is the theft of petrol ... is quite likely rising and it's an issue I think we need to look at,'' she said.