Police are treating a knife attack at a western Sydney church as a terrorist act.

A 15-year-old boy has been arrested after a stabbing at an Orthodox Assyrian church in western Sydney which sparked unrest as an angry mob confronted police.

New South Wales Police Commissioner Karen Webb said the boy allegedly made comments as he launched the attack.

“After consideration of all the material, I declared that it was a terrorist incident,” she told reporters on Tuesday.

The boy arrested was on a good behaviour bond after facing court for a knife crime just three months ago, reports ABC.

The ABC said that he was charged with a number of offences, including possessing a knife last year after an incident at a train station with other boys in Sydney.

The teenager was arrested at the church after being held down by members of the church, and was also hospitalised for finger injuries, local media reported.

NSW Premier Chris Minns urged calm on Monday night after the stabbing of Bishop Mar Mari Emmanuel at the Christ the Good Shepherd Church in Wakeley - an incident broadcast on the church’s livestream.

“Those violent pictures are probably what caused the uproar in the community - people saw that, responded and unfortunately we ended up with a public order incident,” NSW acting Assistant Commissioner Andrew Holland told reporters.

A person dressed in black is seen approaching and stabbing the bishop multiple times to the head and upper body at the altar as parishioners screamed and ran to the cleric’s aid.

The suspect was “known to police,” Holland said, and not a regular attendee at the church.

Prime Minister Anthony Albanese addressed the Sydney church attack, confirming last night is being treated as a terror incident.

“There is no place for violence in our community, there is no place for violent extremism we are a peace-loving nation.”

Minns said the scene was disturbing but urged calm, adding that he convened a meeting of faith leaders representing religious communities across western Sydney late on Monday night.

He said they “endorsed and supported a unanimous condemnation of violence in any form, called for the community to follow first responder and police instructions and called for calm in the community”.

“We’re calling on everyone to act with kindness and respect for each other,” he said.

Bishop Mar Mari Emmanuel of the Christ the Good Shepherd Church in Wakeley, NSW was stabbed during a livestreamed church service.

NSW Ambulance said they were called to the church about 7.15pm and sent multiple paramedics to the scene.

NSW Police said two clergyman were taken to hospital.

The church said Bishop Emmanuel and a senior priest were in a stable condition and also appealed for calm.

“We ask for your prayers at this time,” the church said in a statement posted on social media.

“We also kindly ask anyone at the church to leave in peace as our Lord and Saviour, Jesus Christ, teaches us.”

Holland said a 15-year-old suspect “sustained injuries to his hand as a result of his actions”.

He said the stabbing suspect was held down by parishioners of the church until police arrived.

“Police were in the process of conveying the young person from the church when it was identified a large group had gathered outside,” Holland said.

“A decision was made to retain the young person in the church for his safety”.

The crowd continued to build outside the church and “a public order incident developed requiring police from all regions across Sydney”.

NSW Premier Chris Minns, NSW Police Commissioner Karen Webb and Ambulance Commissioner Dominic Morgan speak during a press conference in Sydney following a stabbing at a church in Wakeley, which was followed by riots. Photo / Getty Images

Holland said more than 100 police officers and 30 police vehicles attended and the suspect was later removed from the church.

Two police officers were taken to hospital after being injured by members of the crowd who broke into “a number of houses to gain weapons to throw at the police”.

Several police cars were damaged.

Holland said some in the group also threw items at the church in a bid to get access to the suspect.

“They need to let police to do their jobs and let us do the investigation,” he said.

“Police will make arrests in the future in relation to this public order incident,” Holland said.

This article was originally posted on the NZ Herald here.