On Friday 08 March between 1800hrs and 1830hrs a white van and a grey car were seen loading a JCB 360 excavator onto a trailer that was being towed by the van.
This was at a road works site on the A164 between Willerby and Beverley.
A hydraulic jack hammer which attaches to the JCB was also removed.
The theft was discovered on Monday 11 March and inquiries revealed the equipment being moved at the times mentioned on Friday 08 March.
Witnesses are required to the theft. Traffic on the A164 will have been heavy at the time and motorists may well have seen the plant equipment being removed but not been aware that they were being stolen.
Anyone with any information about the missing plant machinery is asked to contact Humberside Police on the non emergency number 101 referring to log 481 0f 11 March 2013 or call Crimestoppers anonymously on 0800 555 111.