Spilled fertiliser caused minor traffic delays on State Highway Three North of Whanganui Monday morning.
Red dust covered much of the road after a truck's trailer overturned on a straight stretch of road, five km north of Maxwell, shortly after 8am.
The driver was not hurt and the truck remained upright.
Police said the cause of the accident was not known at this state.
A nearby farmer said she heard "screeching" followed by a bang.