The cab of an-eight-and-a-half tonne truck has been set alight sometime overnight on Saturday while it was parked outside a house on McKenzie Terrace in Carterton.
Detective Sergeant Rachael Casbolt said the owner of the truck had discovered the burnt-out cab yesterday morning.
"It's obviously happened during the night but at this point we haven't spoken to anyone who saw it, there's been no witnesses at this point in time."
She said a Safety Officer from the Fire Service was investigating the cause of the fire.
"We'll just have to wait for his report," she said.