Seven people were arrested overnight at properties in Flemington, Meadow Heights and Dallas in Melbourne over the alleged plot, which police said was inspired by the Islamic State (IS) group.
Victorian Premier Daniel Andrews described the plot as an “act of evil”, while Victoria Police Chief Commissioner Graham Ashton said police had seized “the makings of an improvised explosive device”.
Speaking at a press conference today, Mr Turnbull said: “Overnight our police and security agencies have disrupted a very substantial terrorist plot.
“Overnight, the Victoria Police, working with the Australian Federal Police and ASIO, have arrested seven persons, five of whom are still in custody, searched five premises and are continuing to search them.
“What they have uncovered is a plot to explode improvised explosive devices in central Melbourne in the area of Federation Square, on or about Christmas Day.
“This is one of the most substantial terrorist plots that have been disrupted over the last several years.”
The raids were part of a counter-terrorism operation involving Victoria Police, the Australian Federal Police and ASIO.
Federation Square, Flinders Street Station possible targets
Commissioner Ashton said it was believed a number of people were intending to carry out an attack involving explosives and other weapons.
“Over the last fortnight … we have had to conduct a criminal investigation relating to the formation of what we believe was a terrorist plot,” he said.
“We believe that there was an intention to conduct what we call a multi-mode attack, possibly on Christmas Day.
Police believe the locations to be targeted include Federation Square, Flinders Street Station, and St Paul’s Cathedral.
Commissioner Ashton said: “We believe [the plot] was going to involve an explosive event, the use of explosives, and we gathered evidence to support that.
“There has also been evidence that we will lead around the possibility of an intention to use other weapons. That could include knives and/or a firearm.”
Commissioner Ashton said four of the people arrested were Australian-born and aged in their 20s.
“The age groups range between 20 and 24 or 25. There is another suspect in this matter who will be charged that was an Egyptian-born Australian citizen. All the others were Australian-born,” he said.
Premier Daniel Andrews said there would be an increased police presence at large gatherings in Victoria over the Christmas period.
“This is not an act of faith. What was being planned, what will be led in evidence, what the police will allege, was not an act of faith, not an act of religious observance, it was, instead, in its planning, an act of evil, a criminal act,” he said.