Australian MP Helen Haines is critically ill in hospital in Melbourne after being hit by a car in what Prime Minister Anthony Albanese says may have been a deliberate attack.

The independent MP, 65, was struck outside her constituency office in Wangaratta, in the state of Victoria, on Monday afternoon.

A man, 43, from the nearby town of Tarrawingee was detained at the scene by a passerby and police say a knife was found in the car.

Police are investigating whether it was an "intentional act" but say they do not believe there is an "ongoing threat to the community".

Political leaders have expressed shock and dismay, with Albanese saying "there is no place for violence in a democracy".

While Albanese said it was too early to understand the motive behind what had happened, he did say the political temperature had been rising in Australia.

His Home Affairs Minister Tony Burke backed up that statement with figures showing that reports of threatening or harassing behaviour towards politicians had risen from 951 to 1,067 in the past year.

Haines was hit by a white Toyota Landcruiser at 15:35 (04:35 GMT) outside her office on Murphy Street in Wangaratta, police say.

The town, which has a population of around 30,000, is a few hours north-east of Melbourne.

A witness told Australian broadcaster ABC they had heard a bang and seen a woman pinned between two cars, external.

Haines was initially taken to a hospital in Wangaratta but later moved to Melbourne by helicopter.

After being subdued and detained by the passerby, the suspect was arrested by police.

Announcing that counter terror police were involved in the investigation, the prime minister said: "This wasn't an accident. There was a deliberate act, it would appear."

In a statement, Victoria Police said: "At this stage, police are investigating as to whether this was an intentional act.

"It is not known yet if the parties are known to each other... The investigation remains ongoing."