It is unclear who the courageous individual is but he managed to create enough distance between him and the attacker to provide some safety in the nail-biting moment.
Two other people have been injured amid reports of a shooting and stabbing in Bourke Street this afternoon.
Breathtaking footage shows the man charging at the knifeman with the trolley as the attacker slashed wildly at two fearless police officers.
@mickh05 added:"Trolley Man is my hero!"
'Cops trying to take down man armed with knife. And I'm thankful for the trolley hero.
Officers were initially called to reports of a auto fire near Bourke Street, a busy thoroughfare, at about 16:20 local time (05:20 GMT).
Sydney/Melbourne - Several people were stabbed in the Australian city of Melbourne on Friday and a man was arrested after an incident in the centre of the city crowded with pedestrians and shoppers.
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A courageous passer-by used a trolley in an attempt to stop a man who attacked police on Bourke Street in Melbourne.
But as the attacks continued unabated, eventually one officer opted for lethal force, shooting the suspect in the chest.
One witnessed tweeted from the scene.
Video taken by witnesses shows a vehicle on fire in the area and bystanders using a shopping trolley and chair to confront the attacker.
Bystander Drew Hair said he was walking on Swanston Street when he heard an explosion.
The witness can be heard screaming as the knifeman gets his weapon just inches from the officer's face.
A small number of people have been treated for stab wounds.
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A second person has been taken to hospital with a head injury, however their condition is not yet known.
They say there is no known link to terrorism at this stage but are "keeping an open mind".
Police said the scene had been cordoned off, and it was being "made safe" by a bomb response unit.
"Passers-by were calling out that members of the public had been stabbed", Supt Clayton said.
They had initially thought the man was running to catch a tram close by, before a nearby police auto rushed to the scene.
He then started attacking people with a knife, stabbing at least three people.
Police have since confirmed three people were stabbed, one fatally.
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