Terror probe after MP critically injured in attack

She will be airlifted to Melbourne on Monday night for further medical treatment.

Police have arrested the 43-year-old male driver and confirmed a knife was seized from inside his Toyota Landcruiser.

It is yet to be determined if the two parties are known to each other, police said.

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.

Authorities are yet to determine the motive for the attack but Mr Albanese said there was "no place for political violence" in Australia.

"This wasn't an accident. There was a deliberate act, it would appear," Mr Albanese told the ABC's 7.30 program.

"We don't know what (the) motivation is. So that is the work that's being undertaken."

The prime minister said he was not personally aware of any personal threats being made against Dr Haines.

Victoria Police Acting Superintendent Ashley Mason thanked members of the community who had stepped in to help.

"This would have been a tragic, horrific incident for people to witness," Act Supt Mason said.

"But I just thank for those that were nearby and those that were involved and assisted in detaining the male, and then also provided any assistance to the injured female."

The attack has been condemned by MPs and senators from across the political spectrum.

"Helen Haines is incredibly hardworking. She is fiercely intelligent, but most importantly, she's just a thoroughly decent human being, full of integrity, and respected right across the parliament," Mr Albanese said.

"She is a well-loved member of her community, and this will come as an incredible shock to that community."

Opposition Leader Angus Taylor said it was a shocking day for the nation.

"No one should be targeted in this way," he said in a statement.

"Australians will be angry and appalled by the attack on Helen outside her electorate office in Wangaratta.

"Our nation cannot become a place where violent attacks are normalised."

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.

Emergency services were called to a crash outside her electoral office on the main street of Wangaratta, in the north of Victoria.

The arrested man is from the nearby town of Tarrawingee, police said.

Dr Haines' family asked Australians to keep her in their thoughts.

"This afternoon, our beloved Helen was involved in an incident outside her Wangaratta Electorate Office, and is receiving medical care," they said in a statement.

"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."