Police have urged motorists to slow down while travelling on the nation's roads this long weekend.
In New South Wales, the road toll currently stands at three, while police have also already issued over 1500 speeding infringements since the annual Operation Stay Alert campaign kicked off.
On Monday, emergency services were called to The Hume Highway Bypass, south of Goulburn, where a Toyota Land Cruiser had hit a guardrail and rolled.
The male driver, female passenger and two boys -- aged six-weeks-old and four-years-old -- were all injured in the crash.
Police have said that the female passenger sustained serious injuries and was airlifted to Canberra Hospital, while the six-week-old boy, who was also taken to Canberra Hospital by paramedics, is in a serious but stable condition.
The male driver and four-year-old boy were treated at the scene of the accident, receiving only minor injuries.
Accident on Hume Highway southbound lane near Goulburn. Four injured pic.twitter.com/XHHrAywizC— Goulburn Post (@GoulburnPost) June 13, 2016
Just before midnight on Friday, a 14-year-old boy was killed when the car he was travelling in crashed near Mudgee in the state's central west.
Emergency services found the car on its roof, while police said that initial investigations suggest that the teenage driver of the vehicle was speeding when he swerved to avoid a wombat and crashed, the ABC reports.
The 16-year-old driver who had been airlifted to Westmead Hospital died on Sunday morning, after having suffered serious head injuries when he was ejected from the vehicle.
The crash happened less than 24 hours after a 45-year-old man died when his vehicle, which was stopped on Henry Parks Road near Orange, was allegedly hit by a passing truck.
Traffic and Highway Patrol Commander Assistant Commissioner, John Hartley, urged drivers to slow down, with speeding infringements up by 743 from 2015.
"Speeding is a risk that can lead to a tragedy," he said.
"Drivers need to slow down and remain alert while on the road. I urge everyone to take care, drive responsibly, respect other motorists and obey the road rules.
In Victoria, there have been five fatalities over the long weekend in four separate crashes, bringing the state's total road toll to 135 compared with 117 at this time last year.
A 45-year old man and a 60-year-old man died when the car that they were travelling in left the road and hit a tree near Maffra in East Gippsland, 220 kilometres east of Melbourne.
The survivor, a 63-year-old man, suffered critical head injuries and was flown to Melbourne Hospital.
In a separate crash, a man died after his car struck a tree at Cowes on Phillip Island in the state's south east.
Emergency crews had to cut the man from his car, however he died a short time later at the scene.
On Sunday evening, a 46-year-old man was killed when the car he was driving rolled over in the rural township of Toolangi, north east of Melbourne.
His passenger, an 18-year-old, was seriously injured and airlifted to a Melbourne Hospital.
On Monday morning, a motorcyclist was killed after a head-on collision with a ute near Wodonga in the state's north.
The driver of the ute was uninjured and assisted police at the scene.
In South Australia, a person was killed after their car collided with a tree and caught fire in Maitland, 168 kilometres west of Adelaide.
After extinguishing the blaze, fire crews found a person's body inside the car.
In New South Wales alone, more than 120,000 breath tests have been conducted with 98 drink drivers charged, while across the state there have been more than 55 major crashes.