A video online appears to show Bishop Mar Mari Emmanuel being attacked during the service at the Christ the Good Shepherd church - barely 48 hours after an earlier mass stabbing attack in the city.

It's not clear what the bishop was attacked with.

Members of the congregation can be heard screaming and rushing to help the bishop.

A man has been arrested, New South Wales Police said.

Four people were injured in the attack, New South Wales Ambulance said.

A man in his 50s suffered multiple lacerations and has been taken to hospital in a serious condition, along with a man in his 30s.

A man in his 60s and a man in his 20s were treated at the scene.

A police statement said: "A police operation is under way in Wakeley, following reports of a stabbing.

"Officers attached to Fairfield City Police Area Command attended a location on Welcome Street, Wakeley, following reports a number of people were stabbed.

"Officers arrested a male and he is assisting police with inquiries."

It comes after six people were killed during a stabbing attack at a shopping centre in Sydney on Saturday.

The attacker was shot dead by an officer who confronted him on her own.