A Darwin contractor was the victim of over $300,000 worth of vandalism on the weekend, after joy-rider broke in and went to town with a bulldozer.

Police say an unknown number of offenders cut the locks of the gate at the Aldabrand Contracting site sometime on Saturday night.

They managed to get into a 30-tonne 980K bulldozer, and used it to wreak havoc on other vehicles in the yard.

But it appears unlikely that this was any normal weekend thrill ride, with evidence that whoever was in the bulldozer had access to a ‘universal key’ to start it, and was experienced in its operation.

The offenders rammed a heavy plant grader, before shunting a pair of water tankers about 30 metres.

They also knocked the top off a fire extinguisher, “causing it to shoot across the compound like a rocket”, according to NT Police Duty Superintendent Louise Jorgensen.

“Offenders have then used the bulldozer to ram a tanker truck to the rear. It then hit another tanker truck in front of it,” she said.

“The vehicles were pushed about 30 metres forward causing substantial damage to both pieces of equipment.

Damage to the grader alone was estimated to be about $7,500 per tyre.

“Total damage caused by this action is estimated to be about $320,000,” Supt Jorgensen said.

“Someone obviously knew what they were doing and knew how to drive the machines,” Aldabrand Contracting spokesperson Bede Skewes has told the ABC.

Speculation abounds as to why the contractor might have attracted a seemingly well-trained vandal, with unproven theories and allegations raised about disgruntled former employees, competitors and even angry environmentalists.