The incident unfolded in the carpark of a Bunnings at Willetton in Perth's south overnight.
WA Premier Roger Cook says the 16-year-old attacked a member of the public before rushing at police officers.
"There are indications he had been radicalised online," Mr Cook told reporters on Sunday.
"But I want to reassure the community at this stage it appears that he acted solely and alone.
Roger Cook says it's believed the teenager was acting alone. (Richard Wainwright/AAP PHOTOS)
"Members of the WA Muslim community, who were concerned by his behaviour, contacted police prior to the incident and I thank them for their help," he said.Â
"Our police responded within minutes, they encountered a very confronting situation but their rapid and professional response kept our community safe."
WA Police Commissioner Col Blanch has watched body worn footage of the incident and says officers were confronted by a male armed with a large kitchen knife.
The teen rushed at an officer holding a Taser, prompting two police to deploy their Tasers but that did not have the "desired effect", he said.
The teen then moved towards a third officer who fired a single shot before being rushed to hospital where he died.
Mr Blanch described the teen as a Caucasian male who was known to police and had complex mental health issues.
When officers arrived at the scene they were unaware another male had been stabbed in the back in the carpark and was now in a serious but stable condition in hospital.
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