The man is believed to be responsible for the slaying a woman in a downtown Sydney apartment before wounding another woman nearby and attempting to stab other people Tuesday.
"A male offender has produced a knife and as a result a female victim, a female member of the public has been stabbed", Superintendent Gavin Wood told reporters a short time ago.
"He was fearless. He was completely fearless", he said, adding that he had "a big scary knife" in his hand.
The suspect turns out to be a mental-health patient who had just recently left a hospital.
"I just thought 'is my brother going to be OK?' as we ran towards him".
A woman, 41, was injured on the street, with police saying she was stabbed in the back.
Police had earlier urged the public to avoid the area around King and Clarence Streets, in the central business district of Australia's largest city, where they were conducting an operation. They were significantly fearless people ... Authorities told the newspaper they do not consider the attack to be terrorism-related, but are investigating.
"To approach a person with a mindset of obviously what this person did, with clear evidence of a stabbing previously, these people are heroes".
Footage of the man's rampage showed him running across a city intersection, his clothes apparently stained with blood.
Roberts, who also gave chase to the alleged offender said the experience was frightening.
Officers are now searching the suspect's home near Blacktown in Sydney's west.
There were unconfirmed reports of other people being stabbed - one fatally.
The situation began just after lunchtime when a man was seen on the streets of the CBD after allegedly stabbing a woman.
One video shows him being pinned to the ground by members of the public while another showed him being led away by police. The Guardian reported the man's pronunciation made him appear like not an Arabic speaker.
Dramatic vision, obtained by 7 News, shows the alleged attacker, covered in blood, being restrained by citizens and emergency services workers.
A witness told Daily Mail Australia she saw fire and rescue workers with an axe and a crowbar join civilians who carried chairs chasing after the man.
"As I'm thinking about doing something the guy jumps on the front of the auto which was on the bonnet over here and then he goes up to the very top".