The collision occurred in the early hours of Thursday morning when a semi-trailer crashed and overturned while travelling south on the Hume Highway.

Another truck travelling in the same direction subsequently collided with the vehicle and emergency services were notified just after 5:00am.

One driver and a third man who stopped to assist on the scene were injured and taken to hospital.

The initial driver was trapped in the vehicle for more than two hours, and was airlifted to Wagga Base Hospital where he is currently in a critical condition.

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Fire and Rescue Regional Zone Superintendent Stewart Alexander was on the scene and confirmed the overturned truck was carrying herbicides.

NSW Police's Crash Unit are currently investigating the cause of the crash, with fire crews planning to start moving the vehicles and containing the chemicals once the investigation is concluded.

Superintendent Stewart said environmental contamination from the cargo is a serious concern but crews have worked closely with the Environmental Protection Agency to secure the trailers.

"Crews will start to render safe the hazardous materials, which are herbicides in the trailers there, once the investigation are done," he said. "Environmental contamination is a concern but we've managed to secure the load and been in close consultation with the EPA to ensure it doesn't get into the waterways."

Once the area is cleared by police, heavy salvage crews will clear the two vehicles and crews will work on the trailers carrying the chemicals overnight.

Superintendent Stewart said they are hopeful one northbound and one southbound lane will be open to allow traffic flow this evening, but the safety of fire crews is top priority.

"It can be a lengthy process to do it safe and right," he said.

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