Footage has emerged of the moments following the shooting at Westfield Hornsby. Courtesy: Nine News

FOUR people have been injured in a shooting outside a shopping centre in Sydney’s northwest after police opened fire on a 23-year-old man carrying a knife.

The man, identified as Jerry Sourian, was seen brandishing a kitchen knife as he wandered around the mall “babbling incoherently”, before he was shot three times by officers.

He reportedly lunged at a female officer after he was told to drop the knife, before she and a male officer opened fire, leaving him with injuries to his arm, thigh and abdomen.

The Daily Telegraph reports Sourian is well known to police and went missing from a psychiatric hospital two weeks ago. Police were informed he was missing on Wednesday.

Nine News has footage showing the moment Sourian ran towards the female police officer. She points her gun at him but the footage does not show the moment police open fire.

WARNING: Distressing content. Stunning vision of the shooting in Westfield #Hornsby. Entire video only in #9NewsAt6https://t.co/m8jbYWUdgS — Peter Overton (@PeterOverton) June 9, 2016

Fragments from police gunfire also injured three female bystanders at Hornsby Mall outside Westfield, leaving them with wounds to their lower limbs and abdomens.

Shoppers fled the scene at the Hornsby Organic Food Markets as they heard gunshots just before midday and saw the ground spattered with blood.

Police confirmed Sourian did not stab anyone and the three bystanders, who include an 82-year-old woman and 65-year-old woman, are in a stable condition in hospital.

Footage from seconds after the shooting shows the female police officer apologising to one of the elderly women who had been shot.

In the footage, blood appears to be pouring from the woman’s leg as the officer rushes over.

“Oh sh*t, I’m so sorry. I’m so sorry,” the officer can be heard saying.

Footage emerges of one of the police officers from the #Hornsby shooting apologising to female victim. #9News https://t.co/hAuZJrUURm — Nine News Sydney (@9NewsSyd) June 9, 2016

A spokesman said tasers and “other options” were available to the two police officers who opened fire but said they had a matter of seconds to make a decision in “life and death circumstances.”

“The officers each fired shots at the offender, he was injured several times,” said a NSW Police spokesman. “Unfortunately, some bystanders were also injured with bullets or fragments. All up we have four people injured.”

He said three women aged between 60 and 82 years of age had been injured and were all now in a stable condition in hospital along with the knifeman.

“The person of interest to us is under police guard and at some stage we will be interested to interview him,” he said.

“I understand he was reported missing from a psychiatric centre yesterday and police were making efforts to find him.

“This occurred in a matter of seconds. I say again, in a life and death situation, as the police had to make a very critical decision on the action they took.”

Three of the injured were taken by road ambulance to Royal North Shore Hospital, where there is a heavy police presence, while a fourth person was airlifted there.

Seven News journalist Robert Ovadia reported that Sourian shouted “Allahu Akhbar” before police shot him, and that he had a history of mental health issues.

Witness and local businessman Geoff Milner told the Hornsby Advocate he saw the man walking through the lunchtime market stalls at around 12pm holding the knife.

“I almost walked into this guy,” Mr Milner said. “I saw this old couple staring at him and that’s when I realised he had a full knife.”

Mr Milner, who runs the Peats Bite restaurant on the Hawkesbury River, went into a cafe to call emergency services but police arrived before he got a chance. Two officers allegedly warned Sourian to drop his knife but he instead lunged at them.

“When I walked out of the cafe he was just standing there, like he was waiting for them,” said Mr Milner. “The female officer asked him to put the knife down and she drew her gun. He lunged at her, he ran at her, then the officers split and sort of stood aside. I heard two shots but he didn’t go down.”

The restaurant manager said Sourian eventually went down, as did an elderly woman, who was apparently hit by a bullet ricocheting. Sourian was seen being treated by ambulance officers for a wound to his stomach and an elderly lady for an injury to her leg.

Witness Raquel Redmond, described Sourian as “zombie-like” and armed with a “small instrument” in an emotional account posted on Facebook.

“I was at the Hornsby Westffield (sic) Plaza shooting this morning and that I am shaky but safe and sound at home,” the Ku-Ring-Gai art teacher wrote.

“I was looking at him thinking how sad it was to see somebody walking as a zombie, his arms were holding down and on his left hand he was holding a small instrument. Then the police, in front of me, came into my focus.

“I run to find a place to hide. From there I saw many police running and holding guns and I heard a woman screaming. Then, there were four very fast shots, result: four people shot .”

David Henry was inside the shopping centre when he heard the shots. “I immediately saw people running. There were a lot of mums with babies, yelling and panicked,” he told news.com.au.

“I ran to the window above the fountain (inside the shopping centre) and saw a police woman holding her gun over the suspect.

“As I got there (the man on the ground) was not very well. He was prostrate ... he was looking around gingerly. There was a lot of blood on the ground.”

A Hornsby resident, who did not want to be named, told news.com.au he spoke to the knifeman shortly before the incident.

“I noticed a chap walking around talking to himself, I do a lot of work with the homeless and I asked him if he was OK, he just looked at me and walked away,” he said. “I noticed that he had a knife but I just thought he was one of the traders.”

“Apart from the babbling, he didn’t look different,” the resident said of the man. “He looked dishevelled, but who doesn’t on a Thursday morning?”

The resident described the knife as quite large, probably at least five inches long, and said it looked like an ordinary cutting knife that you would use in the kitchen.

The resident said he heard a “pop, pop, pop” shortly after he spoke to the man. At that stage the shopper was on one of the higher levels of the centre and looked down to see police standing over the man next to the fountain in the middle of the shopping centre precinct.

James Yeom, who was working at a nearby store, told Seven News he saw two people shot by police in addition to the knifeman, who was shoeless and carrying a kitchen knife.

“They just went down with the shot fire, I think they got shot too, they weren’t able to get up,” he said. “They appeared to be casualties of the shooting.

“A few of my customers came in saying they saw a guy holding a knife and they wanted me to call the police. When I was calling police I went out and was looking for this guy; he showed up in front of me holding a knife.

“A few minutes later police officers showed up and asked him to drop the knife. He refused to drop the knife. They pointed their gun at him and asked to drop knife again, which he refused again. Then they shot him down.

“He looked really depressed. He wasn’t looking too aggressive, he was just wandering around … People realised he was holding a knife, looks like they were maybe calling police just like me, but a lot of people didn’t realise what was happening.”

Four injured at Westfield Horsnby NSW Ambulance confirm paramedics are treating four people for injuries at Westfield in Hornsby.

Mr Yeom said he believed three shots were fired and it appeared police were aiming for the man’s legs. “There were a lot of people here. I think all the people moved back to hospital or something but there are a lot of police officers in the area.”

Nine News said Sourian was seen wandering outside the mall looking “drug-induced and depressed” and was heard “babbling incoherently” just before the incident. Police sources said he was ranting.

The owner of the Blu Water Grill, directly adjacent from where the incident took place, told news.com.au his restaurant was in lockdown shortly after 12.30pm. “It’s chaotic,” he said.

Footage via Westfield at Hornsby next to fountain. Three injured. One gunshot. #9News pic.twitter.com/GPmHH80FpZ — David Henry (@heshootspeople) June 9, 2016

BREAKING: Shooting at #Westfield in #Hornsby. Police on scene after reports man wielding knife. pic.twitter.com/oWrB0waZwD — Gemma Garkut (@gemgarkut) June 9, 2016

"We heard bangs, everyone ducked." Eyewitness Daniel Cohen speaks to #9News following Hornsby shooting. pic.twitter.com/I5IhDjNlzz — Nine News Sydney (@9NewsSyd) June 9, 2016

Heavy Police presence at Royal North Shore Hospital. Three ambulances have arrived under escort with Hornsby victims pic.twitter.com/WRbaYyzzQo — Cameron Price (@campricenews) June 9, 2016

WATCH: Footage emerges of moments after the shooting incident occurred at Hornsby. #9News https://t.co/dNl4Aod3kr — Nine News Sydney (@9NewsSyd) June 9, 2016

Dozens of police officers swarmed the mall after shoppers fled and the area was cordoned off as they began trying to piece together what happened.

A police spokesman said a critical incident had been launched after the shooting left four people injured.

“That investigation will be subject to independent review,” the statement said. “Police are calling for witnesses to come forward.

“Police are not looking for any other offenders.”

Hornsby state Liberal MP Matt Kean thanked police who responded.

“We saw again the bravery of the Hornsby police on display,” he said. “They do an incredible job is extremely tough circumstances.”

A NSW Ambulance spokesman confirmed to news.com.au that multiple ambulances responded to an incident in Florence Street, Hornsby, and they treated multiple patients

A customer service representative at Westfield Hornsby said parts of the shopping centre had been cordoned off.

This is the second major incident to take place in the location in the past three months.

On March 30, there was a knife attack less than 100m away at the popular Kangnam Korean BBQ restaurant, also in Hornsby Mall.

On that occasion, 45-year-old Alexander Villaluna allegedly confronted a couple during their meal. He stabbed Jovi Pilapil, 38, and Keith Collins, 53, with a knife. Mr Collins, from the Central Coast, died at the scene.

Villaluna and Ms Pilapil were married. They separated and Ms Pilapil successfully applied to have an AVO in place against him months before the attack took place.

Witnesses said Villaluna, who was charged the following day with murder and attempted murder, calmly walked outside the restaurant covered in the couple’s blood.

Lifeline: 13 11 14 or www.lifeline.org.au