Five teenagers were charged Thursday following a wave of anti-terror raids across Sydney, as hundreds of police swooped on a network they said posed an "unacceptable risk" to the public.

Police made a series of arrests Wednesday evening while investigating "associates" of a 16-year-old boy who last week slashed an Assyrian bishop in the face during a church sermon in Sydney.

Three of the teenagers were charged Thursday morning with conspiring to plan or prepare for a "terrorist act", police said, while two others were charged with possessing "violent extremist material".

One of the group, who ranged in age from 14 to 17 years old, was charged with "custody of a knife in a public place".

More than 400 officers were involved in the searches at 13 locations across Sydney.

Police allege the teenagers were "religiously motivated" juveniles that were part of a "wider network of associates and peers".

Deputy police commissioner Dave Hudson on Wednesday 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."

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.

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 Australian National Imams Council on Thursday cautioned that high-handed police tactics risked further alienating "disillusioned youth".