A soldier has died as a result of a truck crash at a Sydney army barracks earlier this week, as New South Wales police and Defence continue to probe the cause of the accident.

In a press conference this afternoon, a Defence official revealed the soldier, who had been in a critical condition in a Sydney hospital since the accident on Monday morning (local time), had died today of his injuries.

The Mercedes-Benz Unimog multi-purpose truck careered off the side of the road and rolled several times, throwing all 18 on board from the vehicle.

Three other soldiers remain in hospital, with 14 others being cared for at Holsworthy barracks.

Inspector Steve Blair, of the Metropolitan Crash Investigation Unit, said at the time that officers were confronted with a ''horrific'' scene after the crash on a dirt road during a training exercise.

Of the soldiers admitted to civilian hospitals, two remain in a stable condition.

Lt-Col Hollink said the young Victorian's death had come as a shock to the army community.

"The army is a family, and we are in mourning," he said.

"Our thoughts and prayers are with the soldier's family, friends and mates.

"The family has asked for privacy."

Mr Penpraze was described as a promising young soldier who excelled in his training at the School of Military Engineering.

Had he survived Monday's crash, he could have gone on to be deployed in missions in Afghanistan and elsewhere, helping move diggers from place to place and clearing roads of minefields and IED.

Lt-Col Hollink said investigations into the crash were ongoing and would not say whether speed was believed to have played a role.

- Sydney Morning Herald