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

A 15-year-old boy is in custody on Tuesday after the overnight attack at Christ the Good Shepherd Church in Wakeley where Bishop Mar Mari Emmanuel was stabbed as the incident was broadcast on the church’s livestream.

NSW 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 footage showed a person dressed in black 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.

“We’ll allege there’s a degree of premeditation on the basis this person has travelled to that location, which is not near his residential address, he has travelled with a knife and subsequently the bishop and the priest have been stabbed,” the commissioner said.

“They’re lucky to be alive.”

Ms Webb said the teenager was known to police but was not on a terror watch list. She added that the weapon had been described as a flick knife and detectives were investigating reports the boy lost fingers as part of the attack.

The attack led to street violence nearby the church where hundreds of people gathered and scores of police tried to disperse the crowd during which officers were injured and vehicles damaged.

Acting Assistant Commissioner Andrew Holland told reporters on Monday night the violent images captured inside the church probably caused the uproar in the community.

“People saw that, responded and unfortunately we ended up with a public order incident,” he said.

Also speaking on Monday evening, NSW Premier Mr Minns said the scene was disturbing but urged calm, adding that he had convened a meeting of faith leaders representing religious communities across western Sydney.

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.

Local federal member, Fowler MP Dai Le, has called for more police resources in the wake of the stabbing.

“I know that our police force here are under-resourced,” she told ABC TV on Tuesday morning.

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

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.”

Mr Holland said the teenaged suspect “sustained injuries to his hand as a result of his actions”.

He said the youth had been 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,” Mr 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”.

Mr 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.

Mr 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,” Mr Holland said.