The driver of the car which killed four people in Melbourne's CBD did not hesitate, witnesses say, in what police believe was a deliberate act.
Four people, including a young child, were killed during the incident on Bourke St in Melbourne's CBD, with more - including four more children - in hospital.
At least 20 people were injured, some seriously.
It is believed 26-year-old Dimitrious Gargasoulas, also known as James, was the driver. Police did not confirm his identity.
Police said they shot the suspect before he was arrested at the scene. He was put under police guard in hospital.
Police said they believed the man was involved in a stabbing at 2.15am Friday in Windsor, where he allegedly attacked his brother. It was not terrorism-related, they said.
Victims killed at the scene included a man and a woman both in their 30s, and a child who were killed in different locations along Bourke Street. A fourth person died in hospital later last night.
A three-month-old is being operated on after being rushed to the hospital in a police car and a two-year-old was in intensive care.
Commissioner Ashton said at 1.45pm the vehicle entered the city driving erratically and did "burnouts" on the corner of Swanston and Flinders streets.
"The vehicle proceeded up Swanston Street, then turned left into Bourke Street and entered the mall," he said.
"We suspect that [the driver was] intentionally hitting pedestrians. Travelling at speed right through the mall."
Witnesses said there was "no hesitation" as the car drove into pedestrians, sending "people flying like skittles" and running for their lives.
Mohammed Minhaz was waiting at the intersection of Bourke and Queen streets when he saw the car drive onto the footpath and the pedestrian crossing, hitting three people.
"He hit one person on the footpath."
Jeff Richards was standing in the same area moments prior and said he saw the driver menacingly taunt crowds waiting near Federation Square.
"I was just walking up Queens Street ready to go to Bourke Street Mall and then I saw people running in the opposite direction away from Bourke Street," he said.
Laura Polson was in Melbourne for the Australian Open and said she noticed crowds gathering on the sidewalks.
"It was just the most bizarre sort of thing you could see," she said.
"The man basically left, and that's when we saw the police car come after him, literally just a minute after, and then they just kept on coming and coming.
"Lots of people kept on swarming up to see what was happening because these people who have been injured could have been anyone - it was such a peak time for Melbourne, especially being lunch and being the tennis.
"I'm just absolutely devastated for anyone who's lost someone, because it was just … it was horrific."
Lord Mayor Robert Doyle said he saw the car try and turn down Collins Street from Swanston Street, but the driver was deterred by the bollards in place.
"To our absolute horror we watched him turn back onto the footpath on Swanston St at lunchtime on Friday and accelerated down Swanston," he said.
Another eyewitness named Sian saw the moment the driver veered toward pedestrians.
"There was no hesitation, which is something I've seen in car accidents before and … it was an odd thing to see. He was just collecting people as he was going along they were just flying like skittles basically," she said.
"There was no hesitancy as he got to the crowds, he didn't swerve, he just drove right through them."
Commissioner Ashton said the suspect was known to police and was also charged over an incident last weekend.
"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," he said.
"He has been coming to our attention more recently over recent days in relation to assaults, family violence-related assaults."