Thieves are targeting cars left with their doors unlocked or windows open.
In the past two weeks, police in Chorley have received 14 reports of thefts from vehicles left insecure.
There have been incidents around the borough, with Chorley North West a particular hotspot.
Insp Dave Robinson, from Chorley police, said: “We have recently seen an increase in the number of incidents where the vehicle has been left insecure.
“Obviously it doesn’t excuse what they are doing, but it makes their job considerably easier, particularly if property is on display as well.”
Police are urging drivers to secure doors and windows to prevent thefts.
And they are reminding people not to leave any belongings on display.
Insp Robinson urged drivers: “Be mindful. A lot of these people will try hundreds and hundreds of vehicle doors.”
Extra police patrols are being carried out during the night in the areas targeted as officers work to tackle the problem.