Speed may be factor in army truck rollover

Photographs and video footage of the accident show the truck lying on its side, next to an embankment with military backpacks and other equipment spilling out. (ninemsn.com.au)

Photographs and video footage of the accident show the truck lying on its side, next to an embankment with military backpacks and other equipment spilling out. (ninemsn.com.au)

At least one man remains in a critical condition in hospital after a truck rolled during an army training exercise in Sydney, injuring 18 soldiers.

One man is on life support after an open-top military truck overturned during a defence exercise in Sydney, leaving injured soldiers strewn on the ground, police say.

Metropolitan Crash Investigation Unit Commander Inspector Steve Blair said officers were confronted with an "horrific" scene as the crash injured all 18 people inside the vehicle.

Two men were airlifted to hospital, and one remained in a critical condition, after the truck crashed at about 9am (AEDT) at Sydney's Holsworthy Barracks on Monday, Defence said.

The soldiers were injured when the truck careered off the side of the road and rolled several times, throwing them from the vehicle.

"Things like this, with 18 people, a vehicle overturned, people being ejected from the vehicle, it will look somewhat horrific," Insp Blair told reporters.

He said officers were still at the scene investigating the cause of the crash, but it appeared speed may have been a factor.

At the time of the crash, the truck was travelling in convoy with a support vehicle carrying equipment, Insp Blair said.

He said police would be on site investigating the crash for some time, and would be taking detailed photographs of the scene, looking for skid marks and examining the truck's brake.

The crash was something out of the ordinary for police, he said, as it was on a military site and included so many passengers.

"We are always saying that any collision is bad. We are lucky at this stage that no-one has passed away".

Police said the critically injured soldier was on life support and others were being treated for cuts, bruises and broken bones.

Two of the injured were taken by air to Sydney metropolitan hospitals and 11 were transported by road, Defence said.

Another five defence personnel were treated on site before being transported to the Holsworthy Military Hospital.

The exact details of the injuries are being confirmed.

The critical soldier's next of kin have been notified, with Defence contacting the other passengers' family or friends.

Defence said no personal details would be released at this stage and they would not speculate on the cause of the accident.