Australian police said there is no evidence of a terrorist link to a car ramming attack Thursday in central Melbourne that left 19 people injured.

Police said the driver was a 32-year-old Australian citizen of Afghan descent who has a known history of drug use and mental health issues. The man was known to police for historical minor assault and traffic offences.

"We don't at this time have any evidence or any intelligence to indicate there's a connection with terrorism," said Shane Patton, acting commissioner with Victoria state police.

The streets outside the city's iconic Flinders Street railway station were crowded with Christmas shoppers late Thursday afternoon when a white Suzuki SUV ran a red light and sped up to slam into pedestrians crossing the road before crashing into a traffic barrier.

Members of the public stand behind police tape after Australian police said on Thursday they have arrested the driver of a vehicle that plowed into pedestrians at a crowded intersection near the Flinders Street train station in central Melbourne. (Melanie Burton/Reuters)

While police had earlier said 14 people had been injured, Victorian Premier Daniel Andrews confirmed that 19 people were taken to hospitals. A preschool-aged child was among four people listed in critical condition, Australian media reported.

Andrews described the incident as "an act of evil and an act of cowardice, perpetrated against innocent bystanders."

Suspect drove alone

Witnesses described a horrific scene.

"I was crossing Flinders Street on the way to the train station. I heard an engine rev behind me and heard a thump," one man, identified only as David, said on ABC TV. He said he turned around saw "people literally getting thrown into the air as it hit them."

Bystanders rushed to drag the driver out of the vehicle before police arrived to arrest the man.

Early reports said there were two men in the car, but Patton confirmed the suspect was driving alone.

Confusion had arisen when a second man was seen being apprehended alongside the driver. Patton said this was a 24-year-old man who was seen filming the incident on his mobile phone and found carrying a bag containing three knives.

Patton said that man was taken into custody to determine whether he was connected.

"At this stage we don't believe that to be the case," he said.

No increased danger

Patton said the investigation would involve the force's counterterrorism unit to ensure "that there isn't that connection, and that there is no ongoing threat," but that this was being treated as a singular incident. He said police were working with Australian intelligence agency ASIO, and with Australian Federal Police. There was no intelligence to suggest the man was a person of interest to those bodies, he said.

"We understand he's on a mental health plan and receiving treatment for a mental illness," Patton said.

Patton said that while police numbers would be increased around Melbourne in the coming days, there was no increased danger threat surrounding the city over the busy holiday period.

Australian Prime Minister Malcolm Turnbull sent a tweet calling the incident "shocking" and said his thoughts and prayers were with the victims and those treating them.

As our federal & state police & security agencies work together to secure the scene and investigate this shocking incident our thoughts & prayers are with the victims & the emergency & health workers who are treating them. <a href="https://t.co/JkUM9TuIQe">https://t.co/JkUM9TuIQe</a> —@TurnbullMalcolm

It is the second time this year that Melbourne, regularly ranked one of the world's most livable cities, has been traumatized by a car attack.

In January, six people were killed and more than 30 were injured when a car was driven up a footpath in Bourke Street, near Thursday's incident. Police arrested the driver, who was known to police for a history of illicit drug use, family violence and mental health problems. Police said the case was not terrorism-related.