Prosecutors have described a high-speed crash in which three people died in Melbourne's south-east as the worst example of driving in the state's legal history.

Brazilian national Nei Lima Da Costa, 30, was affected by methamphetamine, also known as the drug ice, when he crashed through the intersection of Warrigal and Dandenong roads at Oakleigh in January.

His rental car was travelling at 120 kilometres an hour, 40kms over the speed limit, and more than 18 seconds after the traffic lights had turned red.

Lima Da Costa's car first struck 45-year-old pedestrian Anthony Parsons, whose body was thrown more than 50 metres by the impact. He died at the scene.

It then travelled into a car carrying five members of the Menelaou family, who were returning from a wedding.

Husband and wife Savvas and Ismini Menelaou, both aged in their 60s, were also killed.

Three other family members including their son, Menelaos, were critically injured.

Lima Da Costa has pleaded guilty to culpable driving causing death and his lawyers have asked the court not to impose a heavy sentence.

But prosecutors said it was the worst case of driving to ever come before a Victorian court.

There were emotional scenes at the plea hearing, with several generations of family members of victims in court to have their victim impact statements read out.

Families will never recover, court told

Through a friend, Sue Parsons, the wife of Mr Parsons, said she would never recover from seeing the most precious person in her life killed in front of her.

Mrs Parsons was several metres behind her husband when he was struck by Lima Da Costa's car.

She said when she ran to his body she thought he was unconscious and tried to talk to him.

The court was told Nei Lima Da Costa had a history of drug-taking. ( Supplied )

But when she asked a firefighter at the scene if she had lost her husband, he told her he was dead.

The couple had been celebrating their 10th wedding anniversary.

Mrs Parsons said she could not forget the vision of her husband's body lying on the road and she could never forgive Lima Da Costa for taking him away.

Members of the Menelaou family also told the court they would never recover.

They said relationships were under strain, businesses were failing, grandchildren of the couple were distressed and they were consumed with fear and anxiety.

Lima Da Costa's lawyer Christopher Dane QC told the court his client was having difficulty communicating.

He said it was hard to understand why the crash happened as Lima Da Costa "has no recollections... he's just shut down".

Lima Da Costa has history of drug use

Mr Dane said Lima Da Costa had a history of drug-taking in Brazil, where he had a 12-year-old son, and his Australian wife is pregnant with the couple's second child.

Mr Dane said if methamphetamine was responsible for Lima Da Costa's driving it was yet another example of the "appalling" effect of the drug on society.

Justice Lex Lasry agreed.

Mr Dane described the crash as "a tragedy of enormous proportions".

"If methamphetamine is at the centre of this tragedy, then the penalties are far too light for trafficking and manufacturing," Mr Dane said.

Lima Da Costa will be sentenced at a later date.