Fire officers have been putting out a blaze on a truck full of milk powder in the Waikato town of Tokoroa.
The truck's trailor, loaded with pellets of milk powder, was found alight early on Saturday morning.
The fire is being treated as suspicious.
Fire Service shift manager Jaron Phillips says the milk powder turned into milk during the fire and has created a mess and environmental hazard.
The Fire Service is also treating a string of minor bush fires lit along the main highway north of Dargaville as suspicious.
Five fires were lit along a 25 kilometre stretch of State Highway 12 between 2am and 4am on Saturday.