Some injured in Sydney in the second three - day incident

A number of people were injured during a knife attack on a church in a suburb of Sydney on Monday, police said.

The officers arrested a male and he is assisting police with investigations, a police spokesman for Reuters said, following the attack on Wakeley, about 30km west of the central business district.

This is the second massive attack reported in just three days in Sydney, after six people were killed in a knife attack at a shopping mall in Bond's area.

Monday's attack occurred during a service at the Christ The Good Shepherd Church in Wakeley, and police were still on the scene trying to control the large crowds assembled for the event.

The injured have suffered injuries and risk to life and are being treated by doctors, police said.

Local media reported that a church leader and some believers were stabbed during a church service.

New South Wales ambulance service said at least four people were injured, including one man in his 50 ' s, who was taken to hospital in serious condition. There are 11 ambulances on the scene.