The middle-aged man who had been stabbed was in a serious but stable condition and appeared to be doing well, the police commissioner said.
The man had suffered a single, possibly two-centimeter stab wound that may have punctured a lung, he said.
Police believe the teenager sent relevant messages to some members of the Muslim community, who immediately called police, he said, without giving details of the messages.
The boy had mental issues but also online radicalization issues, the police chief said.
In the past two years, the attacker had been part of a countering violence extremism program for people who show signs of religious or issues-motivated concerns, he said.
It is not a criminal based approach, but it is a program to help individuals who are expressing ideologies that are of concern in our community. But they may not be committing any crimes.
Police said they did not know what had triggered the attack.
Blanch said it had the hallmarks of a terrorist incident, but he was not making an official declaration right now as he had no concerns about a wider network being involved.
Australian Prime Minister Anthony Albanese said he had been briefed by police and intelligence services who had advised there was no ongoing threat.
We are a peace-loving nation and there is no place for violent extremism in Australia, he said in a message on social media.
