Kiwi truck driver Michael Knowler pleads guilty to crash which killed Jessica West and son Deighton

Jess West and her 5-year-old son Deighton were killed when their car was hit by a truck. Photo / Supplied

An Australian man whose wife and young son were killed in a horror collision near the Victorian town of Ballarat just days after Christmas said his partner's final screams will haunt him for the rest of his life.

Primary schoolteacher Jess West, 37, and 5-year-old Deighton were killed almost instantly when Kiwi truck driver Michael Knowler ploughed through an intersection at Kingston and smashed into the family's car on December 29, 2019, shortly after midday.

Anthony West said he had no time to think and didn't hear the prime mover brake before it collided with the passenger side of the Toyota Wagon where his wife and youngest son were sitting, flipping the car almost five times.

Oakley West, then 9, who was sitting in the back seat, survived but was seriously injured in the crash and spent four weeks in the Royal Children's Hospital recovering from head injuries.

Knowler, 60, pleaded guilty to two counts of dangerous driving causing death and one charge of dangerous driving causing serious injury.

The truck driver told police he was distracted looking at his phone's GPS and saw the give way sign too late.

West told the Victorian County Court on Monday his beautiful family of four had been "cut in half".

Witnesses at the scene of the crash had attempted to shield the panicked father from the carnage of the crash, prosecutor Sharn Coombes said.

Anthony West told the court his "beautiful family of four has been cut in half". Photo / Supplied

"He knew immediately that his son had not survived and slumped to the floor and punched the door before hearing his son Oakley crying," Coombes said.

West said of the moment: "Hearing Oakley crying and murmuring was the only thing that made me not want to die right there and then.

"The sound of my wife screaming moments before impact was the last thing I heard her say.

"The scream lives with me every day," West said in a victim impact statement to the court.

West said his surviving son Oakley had lost his "best mate and his mother who he absolutely adored".

Oakley (left) was seriously injured in the crash which killed his "best mate" and little brother Deighton (right). Photo / Supplied

Jess' parents and best friend also read emotional victim impact statements to the court in which they described the bubbly, kind mother-of-two and a young, sports-mad boy eager to start prep in a few weeks' time.

Ken Shearer, Jess' father, said: "I am broken by this avoidable tragedy."

Chris Pearson, defence barrister for Knowler, said his client accepted he was distracted and unfamiliar with the road at the time of the crash, but was not "flagrantly disobeying the road rules".

The court heard Knowler had written a letter of apology to West in which he revealed his own son was killed in a car crash when the child was eight-and-a-half months old.

Pearson said Knowler had never been involved in a road incident in his 40 years as a truck driver, his prospects of rehabilitation were good and faced deportation to New Zealand upon his release from jail.

Judge George Georgiou will deliver his sentence on March 17.

- Herald Sun