Emergency services said four people are being treated for "non-life threatening injuries" after an apparent stabbing at a church service in Sydney on Monday.

The incident comes just two days after a knife rampage in an eastern Sydney shopping mall killed six people.

A live stream showed Monday's gruesome attack, which took place during a service at an Assyrian church in the west of the city.

A man approached the altar, raised his right arm and slashed at the preacher with a knife, prompting panic and screams among the congregation.

A number of people appeared to rush to help.

The ambulance service told AFP that four men aged between 20 and 70 were being treated for injuries, including lacerations.

Local media said the incident occurred at the Christ the Good Shepherd Church.