Three people died and 20 more were hurt Friday when a car ploughed into pedestrians in the Australian city of Melbourne, but police said it was not a terror attack.
Witnesses described "bodies flying through the air" and people running out of the path of the speeding car in the central shopping area.
Victoria Police's Acting Commander Stuart Bateson ruled out terrorism but said it was a deliberate act in the heart of Melbourne.
"I can confirm that we believe this is connected to an earlier stabbing in the southern metro region," Bateson told reporters.
"We have the offender in custody. There is no further threat to the public at this stage.
"I can also confirm that this is not a CT (counter-terrorism)-related incident," he added.
Bateson said the man was driving in circles at a busy intersection outside the city's main train station in the afternoon.
"We believe this male did some doughnuts at Flinders Street and Swanston Street, turned left into the Bourke Street mall and deliberately drove into the crowd, continued along the footpath colliding with further pedestrians," he added.
YouTube footage showed a maroon saloon car circling the intersection with a driver wearing a light-coloured top half-hanging out of the window.
He gestures to onlooking pedestrians before heading off down a street.
Paramedics said 20 people were being treated and several had serious injuries.
The Royal Children's Hospital in Melbourne said it was treating one critically injured patient and three seriously hurt.
One witness, Kylie Clark, told Melbourne's Herald Sun she saw "bodies flying through the air".
"It seemed to me they (the vehicle that hit people) were being chased by an unmarked police car."
Another witness told the newspaper "he wasn't stopping and people walking were trying to get away and he just kept going and collected people on his way".
A witness, who asked not to be named, told AFP "it was carnage up the footpath".
Television footage from the scene showed a damaged car with the front doors open and the windscreen smashed.
A handcuffed man in his underwear was lying on a footpath surrounded by police.
Other pictures showed what appeared to be a upturned baby pram.
Heavily armed officers were deployed around Melbourne's Bourke Street mall, close to where the Australian Open tennis tournament is being held.
Police were due to hold a press conference in the evening.