MELBOURNE — An Australian man of Afghan descent with a history of mental health issues drove a car into Christmas shoppers in the city of Melbourne on Thursday, injuring 19 people, but police said they did not believe the incident was terror-related.

"At this time, we don't have any evidence or intelligence to indicate a connection with terrorism," said the acting chief commissioner of Victoria State, Shane Patton.

Police said they detained the 32-year-old driver, who also has a history of assault and drug use.

Four of the injured were in critical condition, including a pre-school aged boy who suffered a head injury.

Police also detained a 24-year-old man at the scene who was filming the incident and had a bag with knives. Patton said it was "quite probable" the 24-year-old was not involved.

The men had not been charged and their names have not been released by police.

The attack took place on Flinders Street, a major road that runs alongside the Yarra River in the central business district of Australia's second-biggest city.

Police and emergency services attend to the scene of an incident involving a vehicle on Flinders Street, as seen from Swanson Street, in Melbourne, Australia on Dec. 21, 2017. Reuters TV

Jim Stoupas, the owner of a donut shop at the scene, told Reuters the vehicle was traveling at up to 62 mph when it drove into the intersection packed with people, hitting one person after another.

"All you could hear was just 'bang bang bang bang bang' and screams," Stoupas said in a telephone interview, adding the car came to rest by a tram stop.

If members of the public have video footage or images, which may assist police with their investigation regarding the Flinders Street incident that took place this afternoon, they are encouraged to upload them here: https://t.co/oFfWkid509 pic.twitter.com/HlHsvPQFL4 — Victoria Police (@VictoriaPolice) December 21, 2017

Melbourne has installed about 140 concrete barriers in the city center to stop vehicle attacks by militants similar to recent attacks in Europe and the United States.

In January, four people were killed and more than 20 injured when a man drove into pedestrians just a few hundred meters away from Thursday's attack. Officials said that incident also had no links to terrorism.

Sydney, Australia's biggest city, has also installed concrete barricades in its main pedestrian thoroughfares.

Australia has been on a "high" national threat level since 2015, citing the likelihood of attacks by Australians radicalized in Iraq and Syria.