Police called to Perth school attended by 'radicalised' teen over ...

There are calls for calm after police were called to the Perth high school attended by a "radicalised" teenager shot dead by an officer at the weekend.

Officers flooded Rossmoyne Senior High School today in response to threatening messages that appeared on a school forum overnight.

Police later confirmed the messages were a hoax posted by an account that had been hacked.

"They're not from the individual whom they appear to be from that is being investigated," Police Minister Paul Papalia said today.

WA Police Commissioner Col Blanch called for police to be allowed to investigate and deal with the situation.

"We've got no ongoing threats, this is a call for calm," he told 6PR radio.

Tensions remained high in the community and some parents said they had been keeping their children home from school.

"My son isn't at school today and a lot of his friends, they're frightened," one parent said.

"Just to know why we had a radicalised extremist in the school without anybody being told."

A second parent said "it shouldn't come to something like this for them to have to do something".

"They're [students] genuinely fearing - they just don't understand what's going to happen next," she said.

The school tried to reassure parents in an email today.

"There is no additional threat to the school or our students," the email read.

Investigations into Saturday's attack by the 16-year-old student continue, four days after the Rossmoyne student was shot dead in a Bunnings carpark.

Australian Federal Police were among those at the school today and told 9News the agency was assisting on the case. 

The deputy commissioner of national security has also travelled to Perth. 

The man stabbed by the teenager remains in a stable condition at Royal Perth Hospital.