The Australian authorities filed a "terrorist act" in Melbourne on Friday after police found gas bottles in the suspect's truck.
Australian police said the suspect was of Somali origin and was known to the intelligence services.
"We are now dealing with the incident as a terrorist, the suspect, known to us, was traveling in a four-wheel-drive vehicle loaded with gas flasks," Victoria County police chief Graham Ashton said.
Police said there was no longer any threat to the public in Melbourne, saying it had launched an investigation into the fight against terrorism.
The Australian authorities said that one person was killed and two people were injured in a stabbing carried out by a man during the busy hour in the business district in central Melbourne, pointing out that they arrested a suspect.
Local media published scenes showing a man who randomly assaulted police officers before shooting him.
Witnesses said they heard screams coming from Burke Street and saw smoke rising in the sky as well as a car burning in the same street, the Guardian reported.
