The knife-wielding attacker killed one person and injured two others in a rush hour stabbing rampage in downtown Melbourne Friday, before being shot and captured by police.
Supt Clayton said authorities were not looking for any other offenders.
Australian media identified the deceased suspect as a 31-year-old Somali male.
The police cordoned off the area and warned people from coming near the area.
Instagram user nohsoohyun86 uploaded this shocking video of the incident.
"At this stage we're still encouraging people to go to those events, and it's highly likely we'll have additional police at all of those events", he said. She then turned around to see a vehicle on fire.
Two civilians became involved as well as the two officers, trying to stop the man from his attack.
Horrifying mobile phone footage shared on social media showed a man lunging at police officers with a knife as a auto was engulfed in flames nearby.
The police there issue a statement saying that a auto had burst into flames and that a small number of people were being treated for stab wounds. One of the victims also died, while the two others were hospitalized.
A second person suffered a head injury and has been taken to hospital.
The suspect was was hospitalized in critical condition.
The incident began after the attacker drove his utility vehicle loaded with gas cylinders into a pedestrian as it mounted the kerb and burst into flames around 4.20pm on Friday afternoon. Police are asking for members of the public to avoid the area.
The incident occurred on a section of the busy street that is closed to traffic.
In the past, the Islamic State has claimed responsibility for some "lone wolf" attacks in which the assailant was later found to have no allegiance to the group.
Ashton added that Counter Terrorism Command will investigate alongside Victoria police.
The prime minister, Scott Morrison, released a statement: "I condemn the act of terrorism in Melbourne today that has tragically taken the life of a fellow Australian who has died as a result of this evil and cowardly attack".
The incident occurred on the same street as a deadly vehicle attack in January 2017 that left six people dead and at least 30 others wounded.
Premier of Victoria Daniel Andrews has described the attack as an "evil and awful thing", while also praising the courageous people who were involved in the frightening incident.
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