The condition of Australian MP Helen Haines has improved from critical to serious but stable, five days after she was hit by a car in north-east Victoria.

The Alfred Hospital in Melbourne gave the update on Saturday morning. It was the first improvement reported since Haines was airlifted to the hospital following the incident on Monday.

Haines, 65, sits in parliament as an independent. Authorities say she was deliberately struck outside her electorate office in Wangaratta, north-east of Melbourne. Both of her legs were amputated as a result of the attack.

Her husband, Phil Haines, said on Wednesday that the "horrendous incident" had left his wife with significant injuries. He added that "her heart and her mind" were "in good shape".

Brendan Nugent, 43, was arrested shortly after the incident. Police allege he drove his Toyota LandCruiser into the MP. He has since appeared in court facing three charges: dangerous driving causing serious injury, intentionally causing serious injury, and causing harm to a Commonwealth public official.

Police have said further charges could follow, including attempted murder. Nugent's lawyer told the court his client had "mental health concerns" but offered no further detail.

Victoria Police said its investigation, which is supported by the Australian Federal Police, is continuing and that a motive has not yet been established. Investigators are examining whether drug use or medication played a role. Nugent's family has said they were long-time friends of Haines.

Soon after the alleged attack, Prime Minister Anthony Albanese told ABC television that Australia had seen a "rise in temperature" and "too much shouting, not enough discourse".

Haines entered parliament in 2019 after a career as a nurse and midwife. She is known for positions that include support for stronger climate action.