Willetton knife attack: CCTV unveils how police shot dead teenage ...

A brief late-night triple-0 phone call was the first crucial clue that WA police were about to have a major incident on their hands.

The young caller did not share his name, age or location before hanging up — but he made it clear he was going to commit "acts of violence", according to authorities.

Minutes later, another phone call to police confirmed he meant it.

That second call was from someone in the vicinity of a group of shops on a major arterial road in Perth's south, saying someone was running around a car park with a knife.

Upon hearing that, three officers raced to the otherwise empty Bunnings car park in Willetton.

It was there at 10:15pm last night, the WA Police commissioner said, that a teenage boy confronted them with a large kitchen knife.

CCTV footage recorded from a camera fixed under the front verandah of a nearby business shows the boy jogging through the car park, as a police car circles.

A brief stand-off ensues, after which the boy falls to the ground.

Police have now left the scene at the Bunnings car park in Willetton.(ABC News: Tabarak Al Jrood)

At a press conference almost 12 hours later, police revealed they had shot the boy dead after tasering attempts failed to subdue him.

The footage shows police surrounding the boy before the camera cuts black.

What police didn't know at the time, but learned shortly after, was that the boy had also just stabbed a man in his back before they'd arrived.

That man in his 30s is now in hospital with serious injuries, but he is said to be recovering.

He was not known to his attacker.

Police have yet to release the 16-year-old's identity.

But did they did paint a picture of his behaviour that was extremely alarming.

In fact, sometime in that flurry to respond to the attack, and afterwards, several triple-0 calls were fielded by police from concerned members of the WA Muslim community.

WA Premier Roger Cook said there were indications the boy had been "radicalised" by extreme ideologies online.

Police Commissioner Col Blanch said the boy sent messages to some of those people who then immediately called police.

"I do want to thank members of the Muslim community who did that because that enabled us to identify rapidly who this individual was, and respond as quick as we did," he said.

"We are dealing with complex issues with a 16-year-old male. Both mental health issues but also online radicalisation issues. He is known to police, but we believe he very much is acting alone."

WA Premier Roger Cook flanked by Police Commissioner Col Blanch (left) and Police Minister Paul Papalia (right) at a press conference for the Willetton incident.(ABC News: Rebecca Trigger)

In fact, the boy was known to more authorities than just local police.

Commissioner Blanch said the boy was one of "three or four" young people in WA actively participating in a national support program aimed at countering violent extremism online.

Despite that, it was unfortunately not enough to stop what transpired in the car park on Saturday night.

For the few in that area at the time, it was a confronting scene to witness.

Just a few restaurants and a 24-hour gym were open at the time.

John Chi was on shift last night at the Korean BBQ restaurant Hancookwan when the incident unfolded.

"There was a guy wielding a knife, or an object from what I was understanding at the time, just in the Bunnings car park area," he said.

John Chi said people in his restaurant heard the gunshots.(ABC News: Tabarak Al Jrood)

"The guy chased the police car up all the way into the no entry sign towards the Bunnings car park area and then … the police moved away and called for backup."

Mr Chi said a police car then pulled up on a grassy patch by a nearby bus stop.

"What happened from there was a stand-off with police," he said.

"Two tasers were shot at the person and then the gunshot was fired promptly afterwards, however, there was a bit of distance before all of those were happening — everyone in my restaurant was able to hear the gunshot as well."

A police van at the scene of the incident in Willetton.(Supplied: WAMN News)

The restaurant supervisor said it was not until this morning that he found out the teenager's declared intention of committing acts of violence.

"When he was chasing the police car around, he was holding it [the knife] like around his waist area and then when he was running towards the police car, obviously he was holding it up in the air so that's why the police pulled away," he said.

"I'm just a little bit shocked the person has died, he's 16 years-old, which is quite unfortunate."

Mr Chi said the police presence in the area was huge by the time he finished his shift.

Emergency services swarm an empty car park in Willetton.(Supplied: WAMN News)

"To start off with about I think one police car or patrol car and then it went to maybe two very soon afterwards and then in the span of 10 minutes we had about over another five to six police cars," he said.

"That would escalate over 10 to 20 through the course of 10:10pm to about 11pm.

"By the time I got out of work there was a police car at every intersection up all the way to IGA."

A major investigation is now underway into what led the boy to attack a random person in that car park last night.