It was not yet clear what caused the spill, but the truck had not been involved in a crash, he said.
Around 20 litres of a liquid dye had been spilled over a few hundred metres of road.
No injuries had been reported, but the truck driver had been de-contaminated.
A road clean up crew had also been de-contaminated, Mr Phillips said.
Two Fire Service hazardous materials units were at the scene, where a full de-contamination tent has been set up, along with another three fire crews to deal with the spill.