The 65-year-old Independent Member for Indi reportedly sustained severe lower-body injuries in the incident, with medical teams holding grave concerns that she could lose both of her legs.
First responders were called to Murphy Street at around 3.30pm following reports a pedestrian had been run down.
It is understood Dr Haines was unpacking the boot of her car in a designated parking bay when it has been reported that a white four-wheel drive ploughed into her and she was struck multiple times by the vehicle.
Police took the man into custody, where he remains under arrest.
Detectives have launched an intensive investigation into the circumstances involved, with sources describing the matter as "extremely serious" as investigators probe whether the driver intentionally targeted the politician in a politically motivated assault.
In a brief media conference, Victoria Police Acting Superintendent Ashley Mason confirmed Haines’ injuries and said she would likely be airlifted to Melbourne for emergency treatment.
He confirmed that a 43-year-old Tarrawingee man was detained by witnesses and arrested by police, who found a knife in his car.
The man remains at the Wangaratta police station where he will be interviewed by investigators.
Prime Minister Anthony Albanese told reporters that joint counter-terrorism and major police investigation was underway.
“The Australian Federal Police, Victorian Police and ASIO are working together on this,” Mr Albanese said.
“The joint counter-terrorism team has been activated, but the motive is not known.” He later remarked that “this wasn’t an accident. There was a deliberate act it would appear.”
Dr Haines, who has represented the sprawling north-east Victorian electorate of Indi since 2019, retained her seat at both the 2022 federal poll and last year's election.
The investigation remains ongoing.
Anyone who witnessed the incident, has CCTV or dashcam footage or anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit an online confidential report at www.crimestoppersvic.com.au
