Updated at 15.30
19 people have been injured, some critically, after a car hit a number of pedestrians in the Australian city of Melbourne.
Police said the incident happened on Flinders Street in the city centre, near the city's main railway station, at around 4.45pm local time.
The injured people include a young child, while four of those injured are said to be in a critical condition.
The suspected driver of the car has been arrested, and has been hospitalised.
He was arrested by an off-duty police officer, who has also been taken to hospital in a stable condition.
Police say they believe it was a 'deliberate act', but have yet to establish any motivation behind the incident.
Image: David Clough/PA Wire/PA Images
The arrested man is a 32-year-old Australian citizen of Afghan descent, and is known to police.
Officials say the suspect has "history of drug use as well as mental health issues".
They added: "We don't have any evidence or intelligence to indicate a connection to terrorism. Having said that, however, we continue to support this investigation with our counter-terrorism command to ensure that there isn't that connection and there is no ongoing threat."
Media conference regarding the Flinders Street incident with Commander Russell Barrett. pic.twitter.com/j7zx0V5fYQ
— Victoria Police (@VictoriaPolice) December 21, 2017
Paramedics have now transported 13 people to city hospitals. Two more people are being assessed by paramedics at the scene.
— Ambulance Victoria (@AmbulanceVic) December 21, 2017
A second 24-year-old man was arrested after being seen filming the incident, and was found carrying a bag containing knives.
Police say it is now believed he had no links to the incident, but he is "still assisting police with enquiries".
Pedestrians and drivers were being urged to avoid the area.
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. https://t.co/JkUM9TuIQe
— Malcolm Turnbull (@TurnbullMalcolm) December 21, 2017
Speaking at a news conference, Police Commander Russell Barrett said that while the motive for the incident was not yet clear, police "believe it was a deliberate act".
Footage shot on a mobile phone at the scene shows the driver, with dark hair and a close-cropped beard, being wrestled to the ground and handcuffed by officers.
A member of the public can be heard telling police "he was trying to run away".
The man, who is wearing a white shirt and pale blue jeans, appears to be unconscious as he lies on by the side of the road.
Officers can be seen checking his pulse, and trying to revive him as they turn him onto his back by slapping his face.
They can also be seen checking his jean pockets.
The white SUV can be seen in the middle of the road with its passenger door wide open and its air bags deployed.
The front of the car is completely crushed.
The second man, who was wearing jeans, a dark t-shirt and trainers, was arrested by officers on the steps of the station and can be seen lying on his side as three officers handcuff him.
Injured people can also be seen lying on the road being helped by members of the public, while sirens blare in the background as paramedics approach.
People at the scene have been described as "running towards" the injured on the ground the moment the incident took place.
At the time of the crash, the area was packed with Christmas shoppers including children, who have now finished school for their holiday break.
Reports differ as to the speed at which the car was travelling, with some describing it as not travelling fast, while others say it was travelling at around 60mph (97kph).
Victoria Police are asking witnesses to contact them, and have urged anyone with images or video footage of the incident to upload it to their public evidence website.
Police say they will be putting hundreds of extra officers on the streets over the coming days, but have stressed that there is "no increased threat" to the public.
The Department of Foreign Affairs says anyone concerned about people affected can contact its Consular Division on 01-408-2000.
We are aware of an incident in Melbourne, anyone with concerns about Irish Citizens should contact the Department's Consular Division on 01 408 2000
— DFATravelWise (@dfatravelwise) December 21, 2017
Additional reporting: Jack Quann and IRN