Australian police arrested seven teenagers in a wave of anti-terror raids Wednesday, with top officers claiming the network may have been plotting an attack and posed an "unacceptable risk" to the public.

More than 400 officers were involved in searches at 13 locations across Sydney following the non-fatal stabbing of an Assyrian bishop last week.

A 16-year-old boy was already in custody for that attack but police said seven more "religiously motivated" juveniles that were part of a "wider network of associates and peers" have now been arrested.

Deputy police commissioner Dave Hudson said "intense" surveillance of the network painted an alarming picture that demanded immediate action. 

"Their behaviour, whilst under surveillance, led us to believe that, if they were to commit any act, we would not be able to prevent that," he told reporters after the raids. 

"And we believed, through the investigation, that it was likely that an attack might ensue.

"We considered that the risk was too great," he said.

Police said the offenders were all juveniles aged from 15 to 17.

"The terrorism landscape and the radicalisation of youth online is a continuing problem for us," Hudson said.

Australian Federal Police counter-terror specialist Krissy Barrett said the network "shared a similar violent extremist ideology".

Although police believed an attack was possible, Barrett said they had so far failed to turn up any evidence "of specific locations, times or targets". 

Assyrian Bishop Mar Mari Emmanuel was slashed in the head and chest by a 16-year-old suspect during a live-streamed sermon last week.

- Religious extremism -

Police were quick to describe the teen's actions as a "terrorist" act, fuelled by religiously motivated extremism. 

Hundreds of congregants and members of the community rushed to the site on the night of the attack.

Some hurled rocks and other projectiles that allegedly wounded about 50 police officers, including one who suffered a broken jaw, and damaged several police cars.

Western Sydney has been on edge in the aftermath because community members fear the attack might spark some kind of reprisal. 

Emmanuel has an online following of almost 200,000, galvanising many with his criticism of Covid-19 vaccines and lockdowns as well as Islam.

The area is a hub for Sydney's small Christian Assyrian community, many of whom fled persecution and war in Iraq and Syria.