Firefighters were called to the incident on Culcairn Holbrook Road, near the Culcairn Cemetery Road, about 9.20pm on Thursday night.

Two prime movers and two truck mounted fertiliser spreaders were burning when emergency services arrived.

All four vehicles were completely destroyed by the flames. 

The fire did not spread to grass or any buildings. 

Nine trucks and 15 firefighters from the Rural Fire Service spent hours at the scene, with further resources from Fire and Rescue in attendance.

The fires are estimated to have caused about $1 million worth of damage to the vehicles. 

It was unclear how the blaze started or whether the fires are considered to be suspicious. 

Police are investigating the cause.