The body of the 55-year-old was found at a rest area near Goonoo Goonoo Station on the New England Highway at about 11.45am on Monday.

Oxley Police District officer received a call detailing a concern for welfare from a passerby, who found the body inside the van.

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It's unknown at this stage if the man's death is suspicious, detectives said, but they have established an investigation.

Police said drawers inside of the van had been opened when they arrived, and a generator previously seen there was missing.

Officers are now calling for anyone who may have dashcam footage or who may have seen the vehicle at the rest stop to come forward.

Anyone with information is urged to contact Tamworth Police Station on 6768 2999.

Inquiries are continuing.