At least 14 people were injured -- several of them critically -- after a vehicle struck pedestrians in what police called a "deliberate act" Thursday afternoon in the central business district of Melbourne, Australia, as holiday shoppers lined the streets.

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The driver, who was not immediately identified, was arrested. A second person was also arrested, according to Victoria Police. They have not yet been charged, police said.

Authorities said the incident, which occurred just after 4:30 p.m. local time, was a "deliberate act," but repeatedly said they do not yet know the motivation, including whether it was terror-related.

Based on video footage from the scene, the vehicle was a white Suzuki SUV.

In this photo made video from the Australian Broadcasting Corp., a white SUV vehicle is stopped after allegedly striking pedestrians, Thursday, Dec. 21, 20217, in Melbourne, Australia. Local media say over a dozen people have been injured after a carThe Associated Press
In this photo made video from the Australian Broadcasting Corp., a white SUV vehicle is stopped after allegedly striking pedestrians, Thursday, Dec. 21, 20217, in Melbourne, Australia. Local media say over a dozen people have been injured after a car

Police said at a Thursday evening press conference security would be stepped up in the area, and that the investigation scene would be in place for a considerable amount of time.

In this photo made video from the Australian Broadcasting Corp., emergency medical workers offer aid to victims struck by a vehicle, Thursday, Dec. 21, 20217, in Melbourne, Australia. Local media say over a dozen people have been injured after a car The Associated Press
In this photo made video from the Australian Broadcasting Corp., emergency medical workers offer aid to victims struck by a vehicle, Thursday, Dec. 21, 20217, in Melbourne, Australia. Local media say over a dozen people have been injured after a car

"Police are currently attending an incident on Flinders Street between Elizabeth and Swanston streets where a vehicle has collided with a number of pedestrians," Victoria Police initially tweeted around 5 p.m. local time. "Police have arrested the driver of the car. Extent of injuries are not known at this stage."

PHOTO: First responders in Melbourne, Australia, respond to an incident during which a vehicle collided with pedestrians on Dec. 21, 2017.Rossella Belardi
First responders in Melbourne, Australia, respond to an incident during which a vehicle collided with pedestrians on Dec. 21, 2017.

Pedestrians walk past as police and emergency services attend the scene of an incident involving a vehicle and pedestrians in Melbourne, Thursday, Dec. 21, 2017. Police have arrested a driver after a car drove into pedestrians on a sidewalk in centraThe Associated Press
Pedestrians walk past as police and emergency services attend the scene of an incident involving a vehicle and pedestrians in Melbourne, Thursday, Dec. 21, 2017. Police have arrested a driver after a car drove into pedestrians on a sidewalk in centra

Police said "a number of people were treated at the scene for a range of injuries and have been transported to hospital."

Transit authorities notified riders that routes through the area were being altered.

This story is developing. Please check back for updates.