NSW Ambulance inspector Liam Ryan said paramedics had stabilised two men at the scene of a crash on the Hume Highway.
Both men, aged in their twenties, had been travelling in a rear truck.
The vehicles collided in the northbound lane at about 12.30pm near the Sallys Corner junction, some 50km north of Goulburn, prompting a strong emergency service response.
"One patient suffered chest injuries, while the other was prepared for transport for a suspected spinal injury," Inspector Ryan said.
"We've mobilised lots of emergency services resources for what is a very serious accident. The outcome here could easily have been even worse."
UPDATE: All lanes are open again on the Hume Hwy approaching Illawarra Hwy after an earlier multi-vehicle crash. Traffic remains heavy, so allow extra travel time while conditions ease— Live Traffic NSW (@LiveTrafficNSW) December 2, 2021
One of the trucks caught fire in the crash. RFS crews from the Southern Highlands extinguished the blaze.
Live Traffic reported at 3pm that both lanes had been re-opened but traffic remained heavy. Earlier, one lane of the highway was closed.
Update: 1:50 pm
An Ambulance Media spokesman said critical care paramedics and doctors had been dispatched on two Toll helicopters to the scene. They were treating one male, aged in his twenties, for chest and facial injuries. Another man, also aged in his twenties, was being treated for spinal and abdominal injuries.
Both are in a serious condition and will be flown to Liverpool and Westmead Hospitals.
A RFS media spokesman said one of the two trucks involved in the crash was on fire. Three crews are on scene extinguishing flames from the removalist vehicle.
Two trucks have crashed on the Hume Highway near Sutton Forest.
One northbound is currently closed.
The incident occurred at 12:33 pm.
Two ambulance crews are on scene and two more are en route to the accident scene, reported to be on the Hume Highway's northbound lane, near the Sallys Corner junction at Sutton Forest.
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An ambulance media spokesman said two rescue helicopters were on the way. Two patients have been treated. Injuries are unknown at this stage.
A Traffic Management Centre spokesperson said there was a 4.5km queue of traffic behind the incident.
Motorists are advised to expect delays, slow down and exercise caution.
More to come.