Counter-terrorism authorities are investigating after independent MP Helen Haines was attacked outside her electorate office.
Dr Haines is in a critical condition in hospital after being hit by a vehicle while loading up her car in regional Victoria on Monday afternoon.
A 43-year-old male suspect is in custody.
The national joint counter-terrorism team, including members from the Australian Federal Police and spy agency ASIO, has begun investigations alongside state authorities, Prime Minister Anthony Albanese said.
"It is too early in this investigation for me to provide you with details of what the motivation is behind this attack," Mr Albanese told reporters.
In a statement issued by her office, Dr Haines' family said the 65-year-old was receiving treatment.
"This afternoon, our beloved Helen was involved in an incident outside her Wangaratta Electorate Office, and is receiving medical care," the statement read.
"We thank the swift assistance of bystanders and the dedicated health workers who assisted her, and police for their response.
"Our family, and Helen's staff, will be making no further comment at this time, and ask that their privacy be respected by the public and media.
"Please keep Helen in your thoughts."
Emergency services were called to a crash outside her electoral office on the main street of Wangaratta, in the north of Victoria.
Witnesses have reportedly said the driver of the vehicle had a knife on him which was confiscated by a bystander.
Dr Haines has represented the regional seat of Indi as an independent since 2019, coming to prominence on her platform of political transparency and integrity.