Three people, including a young child, have been killed and a number of others injured after a man allegedly drove into pedestrians in Melbourne's CBD.
At least 20 people have been treated for various injuries after a maroon car ploughed into the crowd just after 1.30pm.
Police said the incident is related to a stabbing in Windsor in inner Melbourne earlier on Friday and is not terror-related.
It's believed the driver was doing burn-outs near Flinders Street Station before they turned onto Swanston Street at around 1.45pm and turned left into the busy Bourke Street pedestrian mall.
The car was then allegedly driven deliberately into pedestrians as it sped along the mall, with people leaping out of the way and running for their lives.
It crossed over Elizabeth Street and mounted the curb, continuing along the footpath hitting more people.
Police shot the driver, who was the only person in the car at the time.
He was arrested near the corner of Bourke and William Streets, seen cuffed on the ground, shirtless and wearing a pair of red underwear.
He is being treated for non-life threatening injuries.
Acting Commander Stuart Bateson from Victoria Police said the incident was not "terror-related".
"We do believe it is connected to an earlier stabbing in the southern metro region," Commander Bateson said.
"If witnesses have left the city, please log your details with Crime Stoppers."
He confirmed the man alleged to be responsible had been arrested and the situation was contained.
Detectives believe the incident is linked to an earlier stabbing.
Police were called to Raleigh Street in Windsor just after 2am today to reports of an argument between two brothers.
One of the men was left fighting for his life after allegedly being stabbed by his sibling.
READ MORE: Melbourne man allegedly stabs brother multiple times in overnight row
Following the stabbing, 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.
Witness Stefano Pavan, from St Kilda, said the driver of the car was near the intersection of Swanston and Flinders Streets.
"He was driving a red car and shouting. Someone was screaming because he was getting crazy," he said.
"He was waving at police from inside the car."
Witnesses reported hearing at least five gunshots before the man was arrested.
"There's someone on the middle of the ground and there's blood all over the street," Rishi Hathiramani, a CBD shopkeeper, said.
"I've seen accidents but never this bad.
"It's pretty brutal."
A number of CBD businesses are in lockdown, while others have been evacuated.
"A heap of people ran into my store, it was horrible. Half of my staff are in tears," a Strandbags manager said.
City office worker William Mulholland said he came out of a laneway and saw a number of bodies lying on the pavement receiving CPR from police and emergency workers.
He said his friend came out of the RACV building on Bourke St and saw a body lying on the pavement in front of him.
"He said he heard two shots, coming from the direction of King St," Mr Mulholland said.
One witness told ABC radio he saw the car travelling along the footpath.
"It was a maroon Commodore travelling easily 70km/hr on the footpath. We heard thumps and there was people flying everywhere," he said.
Another witness was in the Deloitte building on Bourke Street and saw a suspect under police guard.
"The suspect is lying on his back, he's cuffed," he told 3AW.
"There's a crashed car ... completely wrecked and over the top of that car was a pram."
He said he saw a child being stretchered off by paramedics.
Former Victorian police chief commissioner Christine Nixon was crossing the road when the car raced by and had to step out of the way.
Ms Nixon said she saw the pram on the ground and helped the mother.
"I went to a stroller that had been turned over to see if the child was still in the stroller," she told Melbourne radio station 3AW.
"I went there and the child wasn't (in the stroller). It's mother came up and I said 'where's your child?' and she said 'I don't know'. I thought when I turned the stroller over that the child might've been in it but luckily it wasn't."
The car was seen circling the intersection of Flinders and Swantson streets outside the Flinders St railway station minutes before racing up Swantson St and turning into Bourke St.
Pedestrian access has been closed on Bourke Street between William Street and Swanston Streets.
A spokesperson for Victoria Police said the exact circumstances of the incident are yet to be determined.
Trams are not running in both directions.
Read more: Traffic and public transport diverted as police lock down Melbourne CBD
https://twitter.com/VictoriaPolice/status/822285206614704128
Victoria Police is urging witnesses and victims requiring support to call the Victim's Support Helpline on 1800 819 817.