Four people, including a young child, have died and several others have been injured after a car mounted the footpath and hit pedestrians on a busy street in the Melbourne CBD on Friday afternoon.
A man deliberately drove into pedestrians in Bourke Street mall, Victoria police said. The incident was not a terror attack.
In a press conference late on Friday afternoon Victoria police chief commissioner Graham Ashton said the perpetrator was a 26-year-old man with an "extensive history of family violence".
Earlier, police said the incident was connected to a stabbing in Melbourne’s south east in the early hours of Friday morning "involving parties known to one another".
Police were called to a Windsor address just after 2am after reports of two men fighting. Both men had left the scene by the time police arrived, but one of the men presented to a nearby hospital with stab wounds and was in a critical condition on Friday morning.
"Following this incident, it is alleged the same man took a woman... hostage in his car. She managed to escape from the car on the Bolte Bridge earlier today," Victoria police said in a statement.
Video footage shows a red car doing burnouts in the busy intersection outside Flinders Street station on Friday afternoon. The man in the car hangs out the window gesturing to pedestrians and then appears to drive down Swanston Street, which is closed to traffic.
Witnesses say the car then mounted the footpath and proceeded to hit dozens of pedestrians. Others reported hearing gunshots at the scene as the man was detained by police.
Ambulance Victoria said 24 people were assessed by paramedics.
The Royal Children's Hospital released a statement saying it was treating four children and that its emergency department was "very busy".
People in surrounding office buildings saw the driver of the car being detained by police officers near a crumpled red car.
Aerial shots from Sky News showed a baby's pram on top of the car's bonnet.
Former Victorian police commissioner Christine Nixon was at the scene and reportedly helped the mother who owned the pram.
Sharn Baylis, who was on the scene near Bourke Street mall, told BuzzFeed News she saw "about seven people clearly injured" and helped with the most critical person at the time.
Witness Brett Taylor told BuzzFeed News he was about to cross Flinders Street with his partner when the car came screeching into the intersection.
"At first, people didn't realise what was happening and thought it might have been a car accident, or that he was out of control," Taylor said.
"Then as they could see he was doing it on purpose, some people started to move back, to a safer distance, and others started to flee. A lot of people just held their ground and were watching what was going to happen next."
Taylor said the driver was "shouting angrily at everyone" as he drove around the intersection erratically, at one point mounting the kerb.
"He was driving the car aggressively and sticking up his middle finger," he said.
Taylor said that once police arrived at the intersection, the car took off towards Swanston Street.
In a press conference this afternoon Victorian premier Daniel Andrews said the incident was not linked to terrorism or other criminal activity.
Prime minister Malcolm Turnbull praised the professionalism of emergency workers at the scene.
"The professionalism of the police and the 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 own spirit," he said.