The attacker is under arrest and in a critical condition

One person's been killed and two others are in hospital, after a man attacked people with a knife in Melbourne.

Australian police say officers shot the man, who is under arrest and in a critical condition in hospital.

They say the investigation is ongoing but - there's currently no known link to terrorism.

Police were called to an incident on Bourke Street in the city at about 4.20pm local time.

Superintendent David Clayton said investigators are "keeping an open mind".

Superintendent David Clayton address the media in Melbourne | Image via @VictoriaPolice on Twitter

"Nearby police quickly responded to the incident - as they got out of the car, they were confronted by a male brandishing a knife and threatening them.

"At the same time, passers-by were calling out that members of the public had been stabbed.

"Police shot the male in the chest, and he's now in a critical condition under guard at hospital.

"Three people have been stabbed, unfortunately one is deceased at the scene - two other victims are currently in hospital."

Two people, apparently members of the public, came to the aid of police, one using a shopping trolley and another using a chair to try and stop the attacker.