A 22-year-old man charged with committing a terrorist act following a stabbing in Sydney's west was inspired by Isis (Islamic State), police say.

A 59-year-old local man was stabbed several times while walking through a reserve in Minto, around 4pm local time on Saturday.

He suffered injuries to his body and hands and was treated by paramedics and flown by helicopter to Liverpool Hospital, where his condition was described as serious.

When a police officer arrived at the scene, Ihsas Khan allegedly tried to stab the officer before being arrested.

Khan was later charged by the joint counter terrorism team with committing a terrorist act and attempted murder.

Police say the attack was "planned" and "deliberate" despite the victim and Khan being unknown to one another.

"This was clearly a very volatile a very violent situation that police and the members of the community were confronted with," Deputy Commissioner Catherine Burn told reporters today.

The accused allegedly shouted words at the scene, which led police to believe he was inspired by Isis.

"We know that this person has strong religious beliefs inspired by Isis. What made him act yesterday we don't know."

"It was deliberate and it was violent."

Federal Attorney-General George Brandis said police would allege that material related to the terrorist organisation had been recovered in a search warrant of the man's home.

"It is Isis-related material but beyond that I'd prefer, given this matter is still an ongoing investigation, not to be more specific," he told reporters in Brisbane.

Burn confirmed Khan was previously known to police but not in connection with any terrorist group.

"He has had a couple of interactions with local police over matters where we might say his behaviour was odd or unusual.

"He has been of concern, he is a person of concern...

"There may have been some behaviours in the past which might be concerning behaviours but not be linked to any of the matters that we are following or any of the people on our radar," she said.

"This really highlights the challenge that this is the new face of terrorism, this is the new face of what we have to deal with."

A large knife was found at the scene and is under forensic examination .

Media have reported the victim ran into a hair salon after the attack and Brandis thanked bystanders who intervened at grave risk to their own life and safety to help him.

"It may very well be but for the bravery of those citizens to intervene the victim's life would have been lost," Brandis said.

"They are an inspiration to us all, they acted heroically and we should all be in their debt."

Khan was refused bail when his case came up at Parramatta Bail Court today.