Roundup: Motorist who killed 3, injured 20 in Melbourne CBD previously known to police

A young child is among three people who were killed by a motorist who ploughed into pedestrians in Melbourne's CBD on Friday afternoon.

Victoria Police confirmed on Friday afternoon that a man and woman in their 30s and a young child died as a result of the incident while 20 remain in hospital, five of those in a critical condition.

Of the five, one was a three-month old baby who has undergone emergency surgery at the Royal Children's Hospital while a two-year-old was admitted to the hospital's Intensive Care Unit (ICU).

The motorist, who was apprehended by police after being shot in the arm, was being pursued by police when he entered the pedestrian-only section of the Bourke Street shopping mall, causing chaos and hitting dozens of pedestrians.

Daniel Andrews, Victoria's premier, confirmed that the man acted alone and the incident had no connection to terrorist or criminal organizations.

"Our hearts are breaking this afternoon that a number of people died. Others remain in a critical condition, very, very seriously ill, gravely ill in hospitals around our city," Andrews told reporters.

"However, we are stronger than this. We, through our response, through the work of our emergency services, the work that the instinctive way in which Victorians have reached out to support each other, we can be confident that we are stronger than this evil criminal act."

Malcolm Turnbull, Australia's prime minister, praised the bystanders at the scene who provided aid to the injured.

"The prayers and heartfelt sympathies of all Australians are with the victims and the families of the victims of this shocking time in Melbourne today," Turnbull said in a statement.

"We thank and acknowledge the heroism, the professionalism, of the police and emergency workers who rushed to the aid of the victims.

"Joined by bystanders, who mindless of their own danger, sought to help those who had been attacked in this shocking crime.

"Their love, their selflessness, their courage is the very best of our Australian spirit."

Graham Ashton, Chief Commissioner of Victoria Police, confirmed that the 26-year-old man in custody was previously known to police.

"What we do know of the person is there is an extensive family violence history involved. He has come to our attention on many occasions in the past. We have mental health and drug-related issues in the background of this particular person," Ashton said.

"He has been coming to our attention more recently over recent days in relation to assaults, family violence-related assaults. Also was charged by us over the course of last weekend."

The man was wanted by police in relation to a stabbing in the southeastern suburb of Windsor at 2:00 a.m. local time on Friday morning that left the victim, believed to be the perpetrator's brother, in a critical condition.

Ashton confirmed that there was a woman in the car when police first became aware of it but she was released before he reached the CBD.

"When we came across the vehicle, attempting to intercept the vehicle, there was a female in the vehicle. Detectives are still talking to that female but she is not believed to be connected with the offender in the vehicle," he said.

"So we are still working through whether she was a hostage or what the circumstances really were regarding her being in the vehicle, but she was released from the vehicle before the vehicle entered the city." Endit