22/12/2017 12:11 PM AEDT | Updated 22/12/2017 12:30 PM AEDT

'No Terrorism Link' In Melbourne Crash, Turnbull Says

19 in hospital, four critical, after Flinders Street incident.

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The white car involved in the crash, as police and emergency personnel work at the scene in Flinders Street in Melbourne

Prime Minister Malcolm Turnbull has reiterated that police have found no terror links to the driver involved in the Flinders Street crash.

A four wheel drive drove into pedestrians in the middle of the Melbourne CBD on Thursday afternoon, in what police have called a "deliberate act" perpetrated by a man with mental health issues. There have been 19 people taken to hospital, including nine foreign nationals, an 80-year-old man and a four-year-old child. Four people remain in critical condition.

On Friday morning, the Prime Minister gave an update on the incident, stressing that while investigations remain ongoing, police have found no terror links to the driver. Turnbull said the driver, a 32-year-old man of Afghan descent, came to Australia as a refugee "through the appropriate normal refugee programs" and had "a history of serious mental illness and drug abuse."

"He has said, in a number of what the police are describing as utterings, he has said that he attributed his actions to perceived mistreatment of Muslims," the PM said.

"But at this stage, I want to say, I emphasise, at this stage, because investigations are continuing, apart from that statement, there are no known links to any political issues or any, certainly any links to extremist groups, and therefore, the position I am advised off at the moment is that no terrorism link has been identified at this stage."

Turnbull said "nothing should be ruled out" but that initial investigations had not unearthed any terror links.

"Terrorism is politically motivated violence. At this stage, the police are not satisfied they can describe it as that, although he has made reference to the perceived mistreatment of Muslims, as a justification for his actions," he said.

"Now, he has not been formally interviewed yet, but there is no known connection between him and any extremist group. So it may well be that it is ultimately classified as a terrorist act, as a single act of, a terrorist attack, but we had to wait for a thorough investigation. That is being handled by the agencies, state and federal, that are working on the issue right now, even as we speak."

The Prime Minister called it a "despicable and cowardly act" which police were treating as "an isolated incident." Turnbull's comments echo those of Victoria Police Acting Chief Commissioner Shane Patton on Thursday night, who said the driver had a history of mental health issues, and was receiving treatment for a mental illness. The driver was apprehended by an off-duty police officer who happened to be at the scene at the time.

"[The driver] has historical assault matters... He has a history of drug use and mental health issues," Patton said.

"This is early days, but we understand he is on a mental health plan and is receiving treatment and mental illness. We are working through to clarify that. He is still in custody, under arrest for these offences, for what we allege was a deliberate act."

"A range of investigators, including the homicide squad, are being supported by the counterterrorism command. At this time we do not have any evidence for any intelligence to indicate there is a connection with terrorism."