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A 16-year-old boy has been shot dead by police in Western Australia's capital Perth, after he stabbed a man in the back with a kitchen knife.

The boy was rushed to hospital but died. His victim, who was not known to him, is said to be in a serious but stable condition.

There were signs the boy had been radicalised online, state authorities said.

"At this stage it appears that he acted solely and alone," Western Australia Premier Roger Cook said.

Police in Western Australia said they received a call late on Saturday from the teenager who had warned them he intended to commit "acts of violence".

Police commissioner Col Branch told a press conference that within minutes another emergency call was received alerting officers that a "male with a knife was running around the car park" in Willetton, a southern suburb of Perth.

Three officers arrived and found a 16-year-old armed with a long kitchen knife.

The first two officers fired their Tasers but when the teenager continued to approach, the third officer fired a single shot which killed the 16-year-old, the commissioner said.

The teenager was described as a person with "complex issues" who had been involved for several years in an anti-radicalisation programme intended to counter extremist ideologies.

Commissioner Blanch said the incident had the "hallmarks" of terrorism but he was not declaring this as a terrorist attack at this stage.

He also thanked members of the Muslim community who were concerned by his behaviour prior to the incident and had alerted police.