Thieves stripped expensive catalytic converters from eight vehicles stored in the yard of an engineering firm in Whaley Bridge.
The offenders broke into the grounds of Leo Engineering, on the Bingswood Trading Estate, between 5pm on January 8 and 9am on January 9.
They stole parts from the underside of minibuses which were stored within the fenced compound.
Witnesses reported seeing a white van driving near the premises at about 2am on the Wednesday morning and leaving again about 15 minutes later.
A police spokesman said: “Officers are examining CCTV footage and have increased patrols around the site while the firm has installed extra security measures including razor wire fencing.”
Anyone with information should call police 101 or Crimestoppers on 0800 555 111.