© Yik Yeung-manPolice officers cordon off the scene at the mall in Diamond Hill.
Viral video footage of the crime taken from a security camera at the Plaza Hollywood mall in Diamond Hill shows the man coming up behind the two shoppers shortly after 5pm and repeatedly stabbing one of them in a sustained attack that goes on for nearly a minute.
Nobody comes to help for the duration of the attack as the second woman tries to intervene again and again, only to be slashed at and stabbed herself. Police later said the two women, aged 22 and 26, were unconscious when they were taken to United Christian Hospital, where they succumbed to their injuries.
Another video clip that went viral online shows a team of police officers with shields and pepper spray approaching the assailant and ordering him to drop the 15cm knife. They rush him together, dragging him to the floor and handcuffing him.
One woman was stabbed more than 25 times.
The 59-second clip of the attack shows the second woman pushing away the man and trying to drag the injured victim to safety, but the knifeman catches up and continues his onslaught.
The second woman bravely kicks out at the attacker while pulling her injured companion along, leaving a trail of blood on the floor.
The footage also shows the man lashing out at the second woman and then stabbing the first victim multiple times. The second woman comes back and kicks the attacker.
By this point, the first victim is left lying motionless on the floor while the attacker chases after the other woman.
A source similar with the case said the suspect, 39, had a history of mental illness and sought a consultation with a doctor. He said police were also investigating if the suspect knew the two victims.
Footage circulating online shows the suspect buying a knife from a shop about 10 minutes before the attack.
Saleswoman Joy Luk, 54, said the assailant stood beside the two victims as mall medical workers arrived at the scene to provide first aid. Police arrived at the scene shortly after the first aiders.
"I'm still confused. There was no sign the medics knew the assailant was next to them," Luk said. "When the mall notified us to close the shop, we were still clueless about what had happened."
The area was cordoned as officers carried out an investigation.
The suspect was taken to Wong Tai Sin Police Station and is being held for questioning. Detectives from the Kowloon East regional crime unit are handling the case, which has been classified as murder.
The Hong Kong Red Cross urged people not to repeatedly watch clips of the attack on television or social media to avoid emotional distress.
Quoting its clinical psychologists, the organisation said it was normal to feel distress after hearing about the attack or watching the footage.
"If children have watched the clips, parents can first calm them down and explain what happened in a clear and understandable manner," its spokesman wrote on a social media page. "Both adults and children experiencing apparent emotional distress can seek professional help."
Attack occurred on third floor of Plaza Hollywood mall
Office worker Christine Chan, 29, was in the mall at the time of the attack although she did not witness it.
"It was really shocking news. I was startled when news push notifications arrived on my phone," she said, adding that her first response was to think of ways to better protect herself in the event of such an attack happening again.
Lawmaker Bill Tang Ka-piu, who sits on the Legislative Council's security panel, called the case "extremely shocking" and said it was hard to imagine such a heinous crime would happen in Hong Kong.
Tang of the Federation of Trade Unions said it was "undeniable" that some residents felt the city was less safe than before.
The only way to ease people's concerns, he said, was to make the findings of the police's investigation public as open as possible.
Fellow lawmaker and former security minister Lai Tung-kwok said he was shocked such an incident happened in broad daylight.
Lai said he believed the public's concerns over the city's safety would be eased if police could crack the case as soon as possible, which he was confident about.
Between January and March this year, police handled six reports of homicide. Seven cases were reported in the same period last year.
Comment: It's notable that attacks similar to that reported above have, at times, been occurring in clusters: