Teen Arrested Over Fatal Scientology Stabbing Was Trying To See His Mum

A teenager in custody over the fatal stabbing of a "beloved" member of the Church of Scientology in Sydney was believed to be trying to see his mum. 

NSW Police said the teenager was asked to leave the religious centre in Chatswood about midday on Thursday and while being escorted down the driveway he produced a sharp 25-centimetre long kitchen knife.

"With that knife, he stabbed a 24-year-old ... Taiwanese male in the neck and he also caused lacerations to an older gentleman also escorting him from the premises," Detective Chief Inspector Simon Jones told reporters.

The church's security alarm rang out at the bush-enclosed property on Greville Street for 10 minutes before an unmarked police car arrived, neighbour Sharon Schwartz later told reporters.

Police officers arrested the 16-year-old after drawing their stun guns as ambulance and fire crews arrived on the scene.

The two injured men -- who police described as Scientology employees -- were taken to Royal North Shore Hospital.

The 24-year-old died at the hospital. The other man, aged 30, is in a stable condition.

READ MORE: One Dead After Stabbing At Church Of Scientology

"The victim was a beloved member of our church (and) the church is providing the police with any assistance needed in their investigation," a Scientology spokeswoman said in a statement.

The alleged attacker was asked to leave the centre "only and solely in relation to a domestic incident" Det Chief Insp Jones said.

It's thought the 16-year-old had a family member who attended the centre and was at the facility on Thursday.

Det Chief Insp Jones said the assailant was of "Asian descent". News footage showed him being led away by police with his cuffed hands inside evidence bags.

A young Scientologist, who asked not to be identified, told AAP his mum was inside the facility and he'd been stopped from entering to see her.

"I came down when the first (media) camera crew showed up but I was told it wasn't a huge deal," he told AAP. He was not initially aware two people had been stabbed.

"It's a huge building, a lot of people come from around Asia to study here," he said.

"It offers a lot of services other (Scientology properties) don't."

The massive 13,500 square metre building -- which was opened in September 2016 -- is the largest Scientology centre outside the United States.

The site formerly housed the National Acoustic Laboratory and was purchased by the church for a reported $37 million in 2014.