The blaze on the Newell Highway about 40km north of town caused traffic chaos, forced the closure of the major arterial route for most of the day, and also sparked an environmental hazard.

The B-double, headed north from Moree, was laden with dangerous chemicals when a fire was sparked just after 4am.

The RFS were called to the scene before Fire and Rescue NSW crews were deployed to back up firefighters because of the dangerous load.

"It was a mixed load of possible dangerous goods, it was carrying a number of different things, and nothing in large quantities," Fire and Rescue NSW Inspector Rod 

Chetwynd said.

"There were substances if mishandled or were to escape could cause a potential environmental hazard.

"We took early action and sent a crew from Moree and the hazmat crew from Narrabri."

Within minutes the fire engulfed the truck and its load, leaving a blackened shell, with the goods threatening to ignite.

The blaze took off in the dry conditions and spread to nearby paddocks, leaving crews to also battle the expanding grassfire.

Lengthy detours were set up to divert traffic but the clean-up operation took longer than usual with fears the load and the water used by fire crews to douse the blaze could contaminate the area.

"The Environmental Protection Authority (EPA) and the RMS are responsible for the remediation of that site," Inspector Chetwynd said.

"Because of the nature of the mixed load, crews could not determine what the runoff water contained.

"On the advice of the EPA and RMS we're just working with them to make sure it is safe and any area of possible contamination is treated and removed."

A south bound lane reopened to traffic late yesterday before all lanes were cleared last night.

Investigations into the fire are continuing.