It was the second reported mass stabbing in just three days in Sydney after six people were killed in a knife attack at a mall in the Bondi area.

Officers arrested a man and took him to an undisclosed location following the attack in Wakeley, about 30 km (18 miles) west of Sydney's central business district.

A large crowd quickly gathered outside the church after the attack, throwing rocks at police and demanding they bring out the perpetrator, according to two witnesses.

Police fired pepper spray as they pushed back people onto nearby streets, according to a Reuters journalist. More than 100 police officers were ultimately called in to deal with the unrest, and two were taken to hospital with injuries.

Monday's attack happened during a service at an Assyrian church called Christ The Good Shepherd Church.

Videos of the incident circulating online showed the bishop of the church, Mar Mari Emmanuel, standing at the altar of the church and speaking to worshippers as another man wearing a black jumper walks towards him and attacks him.

Horrified members of the congregation scream as the man stabs the priest several time in the chest, the videos show.

The church streamed the sermons live on its social media page. The motive of the attack is unknown.

The church said in a Facebook post that Emmanuel and a priest, Father Isaac Royel, were among the injured.

"We ask for your prayers at this time. It is the Bishop's and Father's wishes that you also pray for the perpetrator," the post said.

The wounded suffered non-life threatening injuries and were being treated by paramedics, police said.

The New South Wales ambulance service said at least four people were injured including a man in his 50s who was taken to hospital in a serious condition.

"There was so much anger because the bishop is loved by them, he's loved by myself as well, he preaches about the Lord and we love the Lord,” said a local resident who gave her name as Canny, and who saw the bishop put in an ambulance.

Emmanuel was ordained a priest in 2009 and then a bishop in 2011, according to the church's website. The bishop appears to be a popular figure on social media, with clips of his sermons garnering millions of views on platforms including TikTok.

Emmanuel became well known for his hardline views during the pandemic, local media reported at the time, with the bishop describing COVID lockdowns as "mass slavery".

A recent sermon posted online by fans shows him claim the United Nations was founded by Satan.

The attack drew condemnation from figures in the city's Jewish and Muslim communities.

The Australian National Imams Council said the attacks were "horrifying and have no place in Australia, particularly at places of worship and toward religious leaders".

"Extremely concerning scenes at a Sydney church," the Australian Jewish Association said in a social media post.

"Our thoughts are with our Assyrian friends."

New South Wales state Premier Chris Minns said in a social media post: "It's important that the community remain calm and continue to listen and act to the directions of Police and Emergency Services."