The stabbing at Christ the Good Shepherd Church in Wakeley left Bishop Mar Mari Emmanuel and a priest hospitalised after a knife-wielding attacker struck during a live-streamed sermon.

It was declared an act of terrorism on Tuesday, however the alleged attacker - a 16-year-old with a history of knife-related crime - is yet to be charged.

He was under police guard in hospital and was likely to remain there for a number of days, NSW Police Commissioner Karen Webb said.

The incident met the criteria to be declared an act of terrorism, which granted police enhanced powers, but it remained to be seen if the teen would be charged with terrorism offences, she said.

The teenager's family have moved out of their home following intense media interest and threats of reprisal attacks on Islamic religious centres after the stabbing at the Assyrian Christian church.

Lebanese Muslim Association secretary Gamel Kheir described the boy's father as distraught, adding he had seen no warning signs from his son in the lead-up to the stabbing.

"(The father) was distraught ... he would not go home, he was too scared to go home," Mr Kheir said.

"Did he see the signs? He said no.

"All he saw was a troublesome teenager who wasn't listening to his father."

The religious leader called for the community to stay united and "not let division into our hearts".

"We're all suffering, we're all feeling the pain ... our communities are on edge as it is, the last thing we needed was this," he said.

Mr Kheir called for the creation of a safe space where potentially troubled young people in the community could be mentored and monitored so that they did not develop radical views.

"We're not denying that we have a problem ... we're not going to bury our heads in the sand either," he said.

Ms Webb also called for community cohesion, describing the events at the church as "one person acting alone and not about one community versus another".

Bishop Emmanuel had a history of sharing controversial views on a range of topics, including criticisms of Islam and other religions, in sermons widely shared on social media.

A candlelight vigil was held outside the church on Tuesday night.

The stabbing triggered a riot outside the church, as some worshippers tried to gain access to the attacker, who was being held inside the place of worship at the time.

The ensuing chaos left several police injured and their vehicles vandalised, while paramedics were forced to shelter in the church.

"We believe that people not associated with the church have turned up as an excuse and become a riot that involved police," Ms Webb said.

Footage from CCTV, police bodycams and helicopters, as well as DNA testing of vehicles, was being used to identify those responsible.

Premier Chris Minns says the police presence will be bolstered across western Sydney and around places of worship for days as "combustible" conditions persist.

Another meeting of the National Security Committee would be held on Wednesday afternoon as federal officials assessed the alleged terror act, Prime Minister Anthony Albanese said.

"Violent extremism has no place in this country," he said.

Footage of the attack and subsequent riots were widely shared on social media, where federal frontbencher and Sydney MP Tanya Plibersek warned lies were being used to divide a reeling city.

"We know there are people deliberately trying to stoke division on social media ... switch it off if you can," she told ABC TV.

Threats had been made against Lakemba Mosque, one of Australia's largest Muslim places of worship, following the church attack.

The Australian Federation of Islamic Councils also condemned the stabbing as an atrocious act.

"Such an act of brutality stands in stark opposition to our cherished values of peace, empathy, and reciprocal respect," it said in a statement urging community members to help with the police investigation.

Australian Associated Press