A young man has attempted to stab a number of people in Sydney's central business district with one woman rushed to hospital covered in blood.
NSW Police on Tuesday afternoon said a man was in custody after a woman was stabbed in a hotel.
She's been taken to hospital in a stable condition with a stab wound to her back.
Multiple police, fire and ambulance vehicles raced to Sydney's central business district at about 2pm, following reports a man was walking along York St armed with a knife.
A short time later, members of the public detained the man before police arrested him.
He has since been taken to Day Street Police Station.
Gavin Wood of NSW Police told media that "most importantly, the threat has 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. They were brave and I can only use that word seriously. They were significantly brave people."
"We don't know the causation or the rationale for his actions today."
Members of the public are being urged to avoid the area.
Witnesses have told AAP a young man armed with a 30-centimetre kitchen knife.
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.
"Please avoid the area," police said on Twitter.
Tejas Oza told SBS News he 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".
If you are struggling mentally contact lifeline crisis support and suicide prevention on 13 11 14 or visit lifeline.org.au.
