About 11am on Thursday, emergency services were called to Cambelego, about 30 kilometres east of Cobar, after a truck carrying ammonium nitrate had rolled.

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Fire and Rescue NSW crews from Cobar, Condobolin, Nyngan, Trangie and Gulgong arrived on the scene to find the truck with its trailer overturned and about 26 tonnes of liquid spilt.

FRNSW Inspector Anthony Hojel said firefighters from both FRNSW and the NSW Rural Fire Service established a 1200m exclusion zone in all directions as they worked to clear the spill.

NSW Police closed the Barrier Highway in both directions near Rosevale Road.

Additional HAZMAT resources also attended to assist.

Crews remained on scene until the spill was contained with sand. The road was deemed safe at about 3.40am on Friday.

It's believed the truck driver was in a stable condition.

The Barrier Highway has opened, however Transport for NSW are urging motorists to reduce their speed and exercise caution.

Fire and Rescue NSW Inspector Anthony Hojel praised crews for their extensive work ensuring the area was safe.

"It was a really well run job," he said.

"It was just a lot of people power required to get the incident back to a safe environment, so that we could open the barrier highway again."

"Crews put fire protection in place during the recovery efforts and also took some gas monitoring, using our detectors to make sure everything was all safe and the surrounding levels of air quality were safe," he said.

Inspector Hojel said a crane and heavy tow truck helped bring the trailer to its wheels and was towed away.