A church leader and three parishioners have been stabbed during a live-streamed service in western Sydney.

A Christian bishop and three churchgoers have been stabbed by a man during a televised service in western Sydney. 

Police said an operation was under way and a man was arrested in Wakeley in the city’s west on Monday night following reports of multiple people being stabbed. 

“Officers arrested a male and he is assisting police with inquiries,” police said in a statement.

Video circulating on social media shows a man dressed in black approaching a man named as Mar Mari Emmanuel, the bishop at Christ the Good Shepherd.

He is seen stabbing the man multiple times to the head and upper body at the altar as parishioners screamed and ran to his aid. 

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

A spokesman said they had treated a man in his 50s for multiple cuts before taking him to Liverpool Hospital. 

A man his 30s was also treated for lacerations and taken to hospital. 

A man in his 20s was being treated for a cut to his hand and a man in his 60s treated for a laceration to his arm at the scene.

-AAP