A molasses truck spilt 2000 litres of the cattle supplement on the New England Highway in Deepwater this morning.
Molasses spilt from hoselines and tanks into drains alongside the road.
While molasses is fed to cattle in diluted form, the supplement is high in urea, making it lethal to animals when concentrated.
Fire services and road authorities were called to deal with the hazardous situation.
The accident was caused, authorities believe, by the truck's bearings or brakes jamming, causing the back of the truck and tyres to catch fire.
The driver pulled up by the side of the road, disconnected the prime mover, and attacked the fire with extinguishers.
The Rural Fire Service from Deepwater put out the fire.
NSW Fire and Rescue built dams across the road drains to stop molasses entering the Deepwater water supply.
Glen Innes Severn Council sucked spilt molasses into container to remove it from the scene, and covered the remainder with sand to absorb it.
Roads and Maritime Services controlled the traffic, and supplied sand to dam the spill.
Police and State Emergency Service also attended the incident.
Topsoil will be removed and completely replaced, to avoid contamination to the environment or to animals.