Three farm tractors and an Isuzu truck have been completely burnt out at a farm on Markeys Road, Marian.
The vehicles had been parked in close proximity of each other in an open area and were last sighted undamaged at 7.30pm on June 16.
They were discovered this morning to be thoroughly damaged by fire and still smouldering.
Nobody has been injured as a result of the fire.
Police and fire investigators are still working to determine the cause of the fire.
Anyone who may have information about the matter is encouraged to contact police as soon as possible.
If you have information for police, contact Policelink on 131 444 or provide information using the online form 24hrs per day.
You can report information about crime anonymously to Crime Stoppers, a registered charity and community volunteer organisation, by calling 1800 333 000 or via crimestoppersqld.com.au 24hrs per day.
Quote this reference number: QP1901169700