What we know about the 'attack' on Helen Haines

The road outside the electorate office of independent MP Helen Haines has become an active police scene after the 65-year-old was allegedly struck by a vehicle this afternoon.

Ms Haines was critically injured in the incident, which has been described by the prime minister as an "attack".

Here's what we know.

What happened?

According to police, initial investigations have determined Ms Haines was struck by a Toyota LandCruiser about 3:30pm on Murphy Street, outside her electorate office in Wangaratta, Victoria.

One witness told the ABC she heard a bang and saw a woman pinned between two cars.

A 43-year-old Tarrawingee man was stopped by a member of the public and has since been taken into custody, police said in a statement.

Police said a knife was found in the vehicle and they were investigating whether the incident was "intentional".

But Prime Minister Anthony Albanese has described the incident as a deliberate attack.

The prime minister told 7.30: "We know that this was a serious incident."

"This wasn't an accident and the suspect is in custody."

It is understood the driver is known to police and will undergo a mental health assessment.

Acting Superintendent Ashley Mason said the scene was "quite dynamic" and that detectives from the Major Collision Investigation Unit would be investigating.

Mr Albanese has said a joint counter terrorism unit had been activated but it was too early to say what was behind the incident.

MP suffers critical injuries

Victoria Police said Ms Haines had suffered critical injuries as a result of the alleged attack.

She was rushed to hospital and flown to Melbourne to undergo emergency surgery for severe injuries to her lower body.

Ms Haines's family has released a statement on the incident, thanking first responders for their swift response and asking for privacy amid the ongoing investigation.

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

"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."

How have politicians responded?

Ms Haines has been described as a respected political figure across party divides.

Mr Albanese has called Ms Haines a "beacon of light" for the regional community in Northern Victoria.

He said Ms Haines was someone "loved and admired because she's someone of integrity".

The prime minister also called for the "political temperature" to be lowered amid increasing rhetoric of violence against representatives.

Opposition Leader Angus Taylor said he was deeply shocked by the incident.

Victorian Premier Ben Carroll said he was "appalled" by the "violent attack" on Helen Haines.

"My thoughts, and the thoughts of all Victorians, are with Helen, her family, her friends, her colleagues and her community," he said.

"I know how devastating this will be for the Wangaratta community and all those who Helen represents.

"Thank you to police, paramedics, firefighters and witnesses for their immediate response.

"An individual has been apprehended, and I thank police for their swift action."