Sydney stabbing LIVE: One dead, one injured as 'lone actor with a butchers knife' brings CBD to standstill

I'm wrapping up our live blog for tonight, but Herald crime reporter Lucy Cormack has collated the most recent developments from today's attack.

She writes that while Mert Ney's screams suggested a possible allegiance to Islamic extremist ideology, police have since seized a phone and USB stick containing information about recent mass deaths and violent acts of white supremacy in the US and New Zealand.

Police said the 21-year-old, who shouted "Allahu Akbar" while wielding a knife in Sydney's CBD, was most likely a troubled man with a long history of mental health issues and no known links to any terror organisations.

It is understood police spoke to Mr Ney's mother at her home in Sydney's west about 3pm today. Police have said the overwhelming amount of news and citizen footage of the incident would be helpful, but it would be Mr Ney’s background over the past year that investigators will look at most closely.

Mr Ney was taken to Royal Prince Alfred Hospital with minor injuries. He is expected to face charges after being formally questioned by police.

Nine News have reported that alleged offender Mert Ney was given a nine month conditional release order for possessing a knife in June this year. 

That order would still be in place today.

Police said they could not confirm details of Mr Ney's criminal history as the matter will soon be before court, but Nine News said they understand he has no other significant offences on his record.

Herald reporter Georgina Mitchell has summarised how Tuesday's "terrifying" attack unfolded in Sydney's CBD.

It only lasted six minutes, but according to NSW Police Commissioner Mick Fuller it "would have been terrifying carnage" when a masked and bloodied man was running through Clarence, York and King streets.

In vision of what followed, the man – wearing a blood-stained grey hooded jumper underneath a black jacket – can be seen frantically pacing on the roadway as he holds a kitchen knife at his side and repeatedly shouts out what appears to be "Allahu Akbar".

Followed closely by a man holding a cafe chair, he jumps onto the bonnet of a black Mercedes on the corner of King and Clarence streets and climbs onto the roof while still shouting, holding the knife above his head.

Uber driver Leon Baghlani was behind the wheel. He was on his way to Macquarie Street with two passengers when "all of a sudden this guy appears with a knife in his hand, covered in blood".

As the man remained at large, he shouted: "Shoot me, f---ing shoot me in the f---ing head".

Neighbours of alleged offender Mert Ney are shocked by the incident that unfolded in the CBD today, reports The Herald's Ben Weir.

Reem Elomair, a neighbour who attended Marayong Public School with Mr Ney, described the 21-year-old as a quiet figure.

"He was not much of a talker. We all used to play with his sister in front of the house, and he would come past and watch,” she said. "He wouldn’t stop and talk, he would just walk past."

Police are waiting outside the home of Mr Ney.Credit: Wolter Peeters

Police did not confirm some media reports that Mert Ney had absconded from a psychiatric unit two days ago but said he was known to NSW mental health services, writes The Herald's health editor Kate Aubusson.

She says today's incident comes two weeks after the Opposition health spokesperson called for an urgent review of the mental health system when a woman was arrested for allegedly cutting off her mother's head.

A veteran psychiatrist working in one of Sydney's largest locked psychiatric wards has cautioned the public against extrapolating damaging judgments linking violence to psychiatric patients.

"We don't know what drove this alleged perpetrator to commit these abhorrent acts, and the fact is people with serious mental illness are far more likely to be the victims of violence than the aggressors," she said.

A senior psychiatrist at a major NSW hospital said patients absconding from psychiatric units was fairly common and acts of violence by these patients was “incredibly rare”.

Herald reporter Ben Weir is at Mert Ney's family home in Marayong, near Blacktown in Sydney's west.

He says a handful of police have blocked off the street but they are waiting for a warrant to enter the house. It is understood they went in about 3pm and spoke to Mr Ney's mother.

One neighbour said he was shocked at the heavy police presence.

Police set up a crime scene at the home of Mert Ney in Marayong.Credit: Wolter Peeters

You can watch this afternoon's press conference below, when NSW Police Commissioner Mick Fuller told reporters the alleged offender Mert Ney "is by definition a lone actor".

"Information was found on him that would suggest he had some ideologies related to terrorism... but he has no apparent links to other terrorist organisations," Mr Fuller said.

A woman, 21, understood to be a sex worker known to Mr Ney, has died after he allegedly stabbed her numerous times in a Clarence Street apartment.

Another woman, 41, is stable in hospital after Mr Ney allegedly stabbed her in the back in a random attack at Hotel CBD. 

When the emergency services presence began to thin after Mert Ney, 21, was arrested on Tuesday afternoon, a young man ran down Clarence Street and grabbed the attention of a remaining officer on the scene.

Herald reporter Jacob Saulwick has the story of how the young man told officers he heard a woman’s screams from inside a nearby building.

He then led police to the front door of the apartment block at 104-118 Clarence Street, where they found the body of a deceased 21-year-old woman. 

The victim, understood to be a sex worker, had reportedly been stabbed numerous times, in a vicious and frenzied manner.

Herald reporter Matt Bungard is at St Vincent's Hospital, where the 41-year-old woman stabbed at Hotel CBD was taken this afternoon.

A spokesman for St Vincent's has told him the woman was responding well but is likely to remain in the hospital for 48 hours. She is currently in a stable condition with two work colleagues by her side.

Police believe she was the victim of a random attack and was not known to alleged offender Mert Ney.

Nine News has obtained CCTV footage that shows Mert Ney running down the street while being pursued by members of the public.

Mr Ney kicks over a bike as some people follow him armed with chairs and others run away. You can watch the footage here: