Mr Blankenstein said the deceased was trapped in the van, and fire crews had to work to remove his body.
The driver of the transporter was uninjured.
Police were investigating the cause of the crash and were attempting to locate and notify family members of the deceased.
Mr Blankenstein said it was raining around the time of the crash.
The road was closed at the junction of State Highways 6 and 65 and traffic between the West Coast and Nelson was diverted. The diversion was likely to remain for some time this afternoon. It adds 90 minutes to the trip from Nelson to Westport.
Today's fatal crash was the second in Buller this month. On October 2, a 66-year-old Seddonville woman, Marie Evelyn Johnstone, died when the van she was driving collided head-on with a car on State Highway 6 in the Lower Buller Gorge.
Her passenger, a 54-year-old man, suffered head injuries.
The woman driving the car suffered chest and leg injuries and had to be cut free. Her 10-year-old passenger suffered minor injuries. They were also from Buller.