Motorists have been warned to be extra vigilant following the rise of petrol tank fuel thefts in Hemel Hempstead.
There was a spate of raids in the Chaulden area in early October when police stepped up their patrols to thwart the crooks.
But in the last week there has been another surge of incidents, prompting Chief Insp for Dacorum Glen Channer to issue a warning to car owners and urge the public to be on their guard.
He said: “These crimes are fairly unusual, and tend to happen during the night.
“To help us catch the people responsible for this we’d ask people to keep an eye out for anyone who may be acting suspiciously around a vehicle.
“If you witness someone underneath a vehicle or tampering with it, please contact police immediately on 999.”
The crimes involve thieves drilling into petrol tanks and draining the contents before making off, leaving the car owner facing a bill for hundreds of pounds worth of damage.
And the thefts are no longer isolated to Chaulden, as cars from Potten End, Fields End and Warners End have been targeted, too.
Nick Reynolds, bodyshop foreman at JFL Crash Repairs in Boxmoor, said: “We’ve had four cars come in from Warners End in the last couple of months.
“It costs around £1,000 for a replacement tank plus labour. We want to warn people and tell them to park their car where they can see it.”
The thieves are also risking lives as well as being caught, because the drilling can cause sparks which could potentially ignite the fuel and fumes, causing serious injury.
Station commander at Hemel Hempstead fire station Dick Lawrence said: “These people are at serious risk of causing an explosion, and endangering the lives of themselves and others around them. It’s extremely dangerous.”