Almost £30,000 worth of damage was caused to vehicles on the Lynn docks at the weekend, police say.
Vandals used a crane to break into the premises on the Bentinck dock sometime between noon on Sunday and 10pm on Monday.
The vehicle was then used to destroy another crane on the site, while five lorries had their headlights smashed and windscreens damaged.
A Norfolk Police spokesman said the cost of the damage had been estimated at more than £29,000.
Anyone who witnessed the incident, or who has information, is asked to contact PC Jamie Haslam, of Lynn police, on 101.