Be alert to radicalised teens: Turnbull

Parents should contact police if they suspect their children are be radicalised, Prime Minister Malcolm Turnbull says.

While Mr Turnbull declined to comment on the case of a Sydney teenager who has pleaded not guilty to planning an Anzac Day terrorist act, he said radicalisation was a "great concern".

"If your teenager appears to be taking an unusual interest in matters of this kind, then that is something that you should share with the relevant authorities," he told reporters in Adelaide on Tuesday.