The accident happened shortly after 7am, when a just-filled diesel fuel tanker travelling on Burley Griffin Way attempted to cross the Hume Highway near Yass in heavy fog.

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Another truck, travelling northbound on the Hume Highway, appears to have collided with the rear carriages of the fuel tanker, rolling the tank, and causing massive damage to the cabin of the northbound truck.

A third truck, also travelling northbound on the Hume, swerved to the side of the road, narrowly missing the accident, but hitting a street sign and ending up stranded in an embankment.

Two utes were also caught up in the accident.

The driver of one of the trucks, believed to be a 45-year-old male, was trapped in his vehicle from the waist down for over two hours. He was conscious when emergency services arrived on scene, however has since been put in an induced coma.

He has since been freed from the crash, and was airlifted by the Snowy Hydro SouthCare helicopter to The Canberra Hospital in a critical but stable condition shortly before 10am. He is believed to have suffered head injuries and internal bleeding.

Three other drivers were treated by paramedics for minor injuries.

Emergency services were working to remove the damaged vehicles and clean up diesel fuel which had been spilt over the road.

Northbound traffic on the Hume Highway is being diverted, and lanes are expected to remain closed until lunchtime.

One southbound lane remains open.

Motorists are advised to avoid the area.