Thieves are targeting cars parked on private driveways to steal catalytic converters.
Since December 19, 14 vehicles parked on driveways in Lynn, Downham and surrounding villages have been hit.
Nine of the vehicles were Ford Galaxy people carriers.
The catalytic converter forms part of the exhaust system beneath the vehicle and contains a small quantity of precious metal such as platinum.
Downham Safer Neighbourhood Team Beat Manager, PC David Mallett, said: “The people stealing these components have no regard for the distress and financial burden placed on their victims.
“The stolen catalytic converters have a modest scrap value, but their theft renders the vehicle unusable and the cost of repairing the damage often runs into many thousands of pounds”