The man who allegedly mowed down 18 people in Melbourne's CBD on Friday, killing three and injuring 15 others, has a history of drug use, violence and psychological problems.

James "Jimmy" Gargasoulas, 26, lived in public housing flats in Windsor, where he allegedly stabbed his brother, Angelo, in the early hours of Friday morning.

A relative said Jimmy has had a drug problem and has been in and out of jail for car theft and drug offences.

"Jimmy has always been a bad person," she said. "I knew it was him. I saw it on TV ... the picture of him sticking his head out when he was doing burnouts.

"I saw a picture and I thought 'Oh My God, that's Jimmy.' I'm shaking. I knew it, as soon as I saw that picture I had this feeling. I can't believe this.

"I balled out crying when they announced that baby died. I'm shaking, I just can't believe this."

Correction: 20 people were injured, not 15

Correction: 20 people were injured when a man driving a maroon car knocked down a number of pedestrians on Bourke Street

We had previously reported the number as 15, based on comments chief commissioner Graham Ashton made at a 5pm press conference. 

However, police inform us that the number injured was actually 20. 

7:06pm: Comment from The Age's top writers

Crime reporter John Silvester writes that the arrested man was deliberately running down pedestrians on Bourke Street. "The extent of damage to the offender's vehicle shows that he hit his victims at speed, with one being dragged under the car and others smashing on the bonnet and onto the roof."

He writes today's events show how susceptible any peaceful city is to random attack and simply cannot be defended.

"The attack on pedestrians by a known violent, charged offender with a history of drugs abuse and mental health problems will lead to calls for the bail structure to be scrutinised in the same way," he writes.

"There will be outrage and calls for major reforms. And this time the law makers will be forced to listen."

Killer driver highlighted how susceptible city is to attack

The Age senior correspondent Daniel Flitton writes the city has been terrorised, although not by an act of terrorism. 

"This might not be an act of politically motivated violence, but the shock and trauma should not be discounted just because it doesn't fit into some grand narrative of global mayhem," he writes. "It is not September 11, 2001, but nonetheless, the dead and injured are someone's sons and daughters." 

7pm: Fifteen people injured, five of them critical.

Fifteen people were injured in the incident, and of these five are currently in hospital with life-threatening injuries. Chief commissioner Graham Ashton has warned the death toll may rise. 

Royal Melbourne Hospital has received 11 patients. Three are critical, two are serious, and six are stable.

The Royal Children's Hospital is treating five people. A three-month-old girl is in a critical condition, two are serious and two are stable. 

St Vincent's Hospital has received six patients. (Condition update to come)

The Alfred has received five patients. (Condition update to come) 

6:29pm: Update: Here are the key facts on the Bourke Street incident. 

6:13pm: Bill Shorten: "All Australians stand with the people of Melbourne"

Opposition Leader Bill Shorten has issued a statement saying "All Australians stand with the people of Melbourne in this horrific moment."

"We offer our heartfelt condolences to the loved ones of the lost," he said in a statement. "We pray for the injured and the frightened, in particular the very young children."

"It's difficult for all of us to comprehend how, why and what has happened. Harder still to understand that it happened here, in a country and a city that prides itself on being such a welcoming, safe and peaceful place."

"Victoria Police have made it clear this was not an act of terror, it was an act of murder. A cowardly, senseless, destructive crime that has claimed the lives of innocent people."

"We wait for answers, we wait for justice and tonight we hold all those in sadness and pain, close to our hearts."

6:01pm: Kids taken to Royal Children's in a critical condition

A three month old baby was in surgery at the Royal Children's Hospital at about 5pm on Friday afternoon, while a two year old is fighting for its in the intensive care unit.

They were among five people, including an adult, injured in the chaos who were taken to the RCH. An additional 20 people have been taken to St Vincent's, Royal Melbourne and The Alfred.

"We received five patients here to the childrens hospital. A three-month-old who's currently in the operating theatre, a two-year-old who is being transferred to the intensive care unit, a nine year old with limb injuries who is being transferred to the ward and a 12 year old who is currently undergoing assessments in the ED department," RCH chief of surgery Mike O'Brien said.

"None of the children have deceased yet but it would be fair to say they are in a critical condition."

The hospital also treated a 23 year old woman with a limb injury, he said.

The RCH did not need to declare a code brown - the highest level of alert - as a result of the incident.

"We've been able to address the situation with the resources that we have at hand and will continue to manage it appropriately," he said.

5:46pm: Premier Daniel Andrews: "our hearts are breaking this afternoon"

Premier Daniel Andrews has called the incident an "evil criminal act" but has thanked emergency services and ordinary Victorians for coming to the aid of those injured. 

"Our emergency services have done us proud in the most difficult of circumstances," he said. 

He said the apprehended man had no links to terrorist organisations or criminal activity.  

"He is no longer a threat to Victorians thanks to the good work of Victoria Police," he said. 

He said stories were emerging of "ordinary Victorians coming to the aid of their fellow citizens" after pedestrians were run down on Bourke Street. 

"Our hearts are breaking this afternoon that a number of poeple have died, and some remain in a critical condition."

"We can be confident we are stronger than this evil criminal act," he said.

5:25pm: Victoria Police Chief Commissioner Graham Ashton on the incident

Victoria Police Chief Commissioner Graham Ashton said three people were killed in the incident - a man in his 30s, a woman in her 30s and a young child. 

"For reasons of family notification I will not give the age (of the child)." 

He said all three were struck in different parts of Bourke Street and were not connected. None of them were in Bourke Street Mall when they were hit by the vehicle. 

Fifteen people were injured by the vehicle, he said.

Of these, five people are in a critical condition, including a three-month-old baby who has been taken to hospital in a police car because there was no time to wait for an ambulance to arrive. 

He said the arrested man had an extensive history of family violence, drug and mental health problems. The man had  come to police attention in recent days because of some assaults.

Chief Commissioner Ashton said people who were also presenting at hospitals with health problems after witnessing the incident. 

5:20pm: Victims Support Helpline

Witnesses and victims requiring support can call 1800 819 817. 

5:19pm: Premier Daniel Andrews addressing the media

"They have apprehended the person involved in this terrible criminal act."

5:11pm: Premier Daniel Andrews to speak on Bourke Street incident

Victoria Police Chief Commissioner Graham Ashton, Premier Daniel Andrews and Ambulance Victoria State Health Commander Paul Holman will shortly be providing an update on the incident. 

5:05pm A walk down Bourke Street in the aftermath of the incident

YouTube user Gerard Hindle has recorded this surreal footage of the scene on Bourke Street in the aftermath of the incident. 

Warning: the footage is rather graphic. This video has since been removed from YouTube, and we have removed the most confronting section of the footage. 

5:00pm: ‘The baby flew into the air’

Dozens of shaken witnesses have gathered at Melbourne West police station to provide statements. One woman, who did not want to be named, said she saw a mother who was pushing her baby in pram struck by the car on the Bourke Street footpath, near Williams Street.

"The baby flew into the air," she said. "The mother was lying on the ground covered in blood."

Police asked the woman and her colleague to get first aid materials and a defibrillator, and she returned to the scene with the equipment. 

She was told that the mother and her daughter were alive one hour after the incident. 

"It was just horrible."

We should point out that while we know a young child has been killed, police have not yet confirmed the child's age. 

4:54pm: Three pedestrians with life-threatening injuries taken to The Alfred

A spokeswoman for the Alfred Hospital said three of five patients being treated there are in a critical but stable condition and two are in a serious condition. 

She said the Alfred hospital was prepared to take more patients, and that staff understood paramedics were still treating some people at the scene. 

Meanwhile, a spokesman for the Victorian health department said no state emergency plans were triggered by the disaster, and that emergency services had handled the situation as well as could be expected. 

At least 25 people have been hospitalised and paramedics are treating more injured people at the scene. 

4:32pm: Victoria Police statement: "one of the deceased is a young child"

Police are investigating the circumstances surrounding an incident that took place in the Melbourne CBD this afternoon.

It is believed police were in pursuit of a vehicle in the CBD when the vehicle deliberately struck a number of pedestrians in the vicinity of Bourke and Queens Streets at approximately 1.30pm.

Police shot the man who was the sole occupant of the vehicle and he received bullet wounds.

He was taken into custody where he is being treated for non-life threatening injuries.

The incident is not terrorism related.

Police understand the incident is linked to a stabbing that took place in Windsor early this morning (20 January) involving parties known to one another.

Following this incident, it is alleged the same man took a woman, who is known to him, hostage in his car. She managed to escape from the car on the Bolte Bridge earlier today.

Three people have been confirmed deceased with more than 20 people injured.

The deceased are yet to be formally identified however police can confirm one of the deceased is a young child.

Police and emergency services remain on the scene and request that people avoid the area.

Police have blocked the Bourke Street between William Street and Swanston Streets including the Bourke Street Mall.

The Homicide Squad will be investigating with the assistance of the Major Collision Investigation Unit.

4:20pm: Arrested man was subject to bail orders

The man arrested over a wild car chase through the CBD that killed three and injured at least 20 more was wanted over a stabbing in Windsor on Thursday and is currently the subject of multiple bail orders.

Police sources say officers called off their pursuit of the man before his car entered the CBD around 1:30pm, fearing it was too dangerous to ram the vehicle.

At least three dead, 20 injured, police lock down city sections

4:15pm: There have been at least 25 people hospitalised. 

Ten have been taken to the Royal Melbourne, six to St Vincent's, five to The Alfred and four to the Royal Children's Hospital.

The RCH will be holding a press conference at 4.45pm.  

Earlier: At least one person has died in a high-speed car chase through the centre of the Melbourne CBD that saw numerous pedestrians run down and gunshots fired, ending with a dramatic arrest on Bourke Street.

About 20 people are believed to have been injured, many seriously.

A maroon-coloured sedan was being pursued by police around 1.40pm when it crossed into the pedestrian-only section of Bourke Street Mall, driving erratically along the popular shopping strip.

Witness Rebecca Russo told Fairfax Media she saw three people hit by the car as it speed through the mall with police in pursuit.

"We were just standing on Bourke Street, and we heard a bit of a crash coming from the mall. I saw a maroon car driving up the pedestrian path on the Flinders Street side.

"People were running out of the way, they were going very very fast. I saw him hit a few people. I saw bodies flying into the air."

Emergency services have reported they are treating of number of injured at the scene, which is outside to the historic Melbourne GPO building.

"All we could see is just the car and carnage, people we're flying everywhere," witness Hank Kerr said in a video posted to Twitter by The Guardian: "Every few metres there's someone badly injured."

The vehicle then crossed over Elizabeth Street, heading west along Bourke Street when other witnesses reported hearing gunshots.

Shortly afterwards, armed police surrounded the maroon car and dragged a single occupant from the vehicle. He was restrained and stripped down to his underwear, according to video and photos posted by observers in nearby buildings.

The vehicle is heavily damaged, with the hood crumpled in and a smashed windscreen.

Video footage taken outside Flinders Street Station shows a maroon car doing "burnouts" in the middle of the intersection of Flinders Street and Swanston Street before speeding north towards Bourke Street Mall.