Charges are yet to be laid after a man was arrested in Sydney's CBD, where a woman was stabbed and another was found dead.
The key suspect in the murder of a 24-year-old woman in Sydney's CBD is under police guard in hospital and the woman is yet to be formally identified, according to NSW Police on Wednesday.
On Tuesday, a woman was found dead and another is in hospital after a 21-year-old man with a large knife went on an alleged stabbing rampage in Sydney's central business district.
NSW Police confirmed on Tuesday afternoon that a man from the western Sydney suburb of Marayong was in custody after a 41-year-old woman was stabbed in a hotel on the corner of Clarence St and King St in the city.
The woman is in hospital in a stable condition with a stab wound to her back.
A police spokesperson also confirmed that the body of a second unidentified woman, 21, had been found inside a unit on Clarence St.
NSW Police Commissioner Mick Fuller told reporters on Monday evening that "all the information that we have at the moment would link these two crimes."
It is believed that the alleged attacker and deceased woman were known to each other through "business purposes", he said.
Commissioner Fuller said the attacks - described as "terrifying carnage" - were subject to an ongoing investigation but were "certainly not a terrorist incident".
The alleged offender was the definition of a "lone actor", he said, and did not have any links to terrorist organisations despite appearing to hold "some ideologies related to terrorism".
"From everything we have at the moment there are no links to terrorist organisations," he told reporters, adding that the man did have a history of mental health issues.
"I can say that he was known to police but his history was unremarkable compared to the gravity of the crimes committed."
Multiple police, fire and ambulance vehicles raced to Sydney's central business district at about 2pm on Tuesday, following multiple reports a man was walking along York St armed with a large knife.
Members of the public rushed to detain the man, using milk creates and chairs, before he was arrested by police and taken to Day Street Police Station on a stretcher.
NSW Minister for Police David Elliot said the "city was safe" and thanked the members of the public who went "well and truly above the call of any citizen".
"There is no reason for any citizen to consider their life in danger and no reason to not continue our lives as usual," he said on Monday evening.
"The city tonight celebrates three brand new heroes."
Deputy NSW Premier John Barilaro echoed the sentiments of his colleague, praising the actions of three members of the public who acted swiftly to apprehend the alleged attacker.
Earlier on Tuesday, Superintendent Gavin Wood said there was only one alleged offender, who was in custody, and that the "threat had been negated".
"A number of members of the public physically restrained the offender. I want to acknowledge those members of the public who got involved," he said.
"They were brave and I can only use that word seriously. They were significantly brave people."
Superintendent Wood said the attacker's rationale was unknown and investigations were ongoing.
Members of the public are being urged to avoid the area.
Witness Zak Barry said he saw the man fall down on York St "and as he's falling he dropped a kitchen knife".
Paul O'Shaughnessy, 37, said his brother Luke, 30, saw a man with a balaclava wielding a knife.
The pair chased the man and then managed to get a grip on him with the help of a third person.
Another witness, Tejas Oza, told SBS News he had just finished a meeting nearby and arrived at the scene as police were arresting a man.
"Police were grabbing him and pushing him on the ground. I heard from people he had a knife in his hand and he was stabbing all these people before police caught him," Mr Oza said.
"I heard this man had basically come out of nowhere and started stabbing people who were having lunch."
He said the crowd was "shaken up, that's for sure".
Video posted on Twitter shows the man yelled at police: "F***ing shoot me in the f***ing head" before he was wrestled to the ground by bystanders and a milk crate was placed over his head.
A witness can be heard saying "he just stabbed a chick in broad daylight".
An Uber driver, Leon, reportedly told 2GB that a shirtless man covered in blood and carrying a knife had leapt across the bonnet of his car.
The caller said the man was being chased by police and firefighters. He said the man appeared to be aged 23 to 24 and looked like he was "on something".
Prime Minister Scott Morrison said his thoughts were with all people "impacted by this violent attack", commending the brave actions of bystanders.
"The motivation for this attack has not yet been determined as police are continuing with their enquiries," he tweeted.
"Any further official information will be provided by the New South Wales Police, who are keeping us appraised through our agencies, including details of casualties."
Federal Labor leader Anthony Albanese also shared his concerns.
"The details aren't fully known yet but we congratulate the NSW Police on the work that they've done and amazingly brave bystanders who took action to apprehend this man," he said.
"Very scary visuals, the fact that people were putting their own lives on the line by taking action was an act of incredible bravery and I certainly pay tribute to them."
If you are struggling mentally contact lifeline crisis support and suicide prevention on 13 11 14 or visit lifeline.org.au.