Police in Melbourne have arrested seven suspects who were allegedly planning a series of Isis-inspired Christmas Day bomb attacks in the city.

The seven had planned attacks on Melbourne's Flinders Street train station, neighbouring Federation Square and St Paul's Cathedral, Victoria state Police Chief Commissioner Graham Ashton said.

Mr Ashton said police had been watching the alleged plotters for some time, and believed they were preparing to use explosives and other weapons.

Terrorism in 2016: Terror attacks in Europe claimed by Isis Show all 9 1 /9 Terrorism in 2016: Terror attacks in Europe claimed by Isis Terrorism in 2016: Terror attacks in Europe claimed by Isis Policemen outside Rouen's cathedral during the funeral of Jacques Hamel, the priest who was killed in a church in Saint-Etienne-du-Rouvray in Normandy on 26 July during a hostage-taking claimed by Islamic State group Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two jihadists, both 19, slit Hamel's throat while he was celebrating mass in an attack that shocked France as well as the Catholic Church Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Muslims place flowers and hold a minute of silence in front of the church if Saint-Etienne-du-Rouvray, western France, where French priest Jacques Hamel was killed on 26 July Charly Triballeau/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two people hold each other by the new makeshift memorial in Nice, in tribute to the victims of the deadly Bastille Day attack at the Promenade des Anglais Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis The Islamic State group claimed responsibility for the truck attack that killed 84 people in Nice on France's national holiday. Mohamed Lahouaiej-Bouhlel, 31, smashed a 19-tonne truck into a packed crowd of people in the Riviera city celebrating Bastille Day Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police work at a site where a Syrian migrant set off an explosive device in Ansbach, southern Germany, on 25 July, killing himself and wounding a dozen others Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis A Syrian migrant set off an explosion at a bar in southern Germany that killed himself and wounded a dozen others in the third attack to hit Bavaria in a week. The 27-year-old, who had spent a stint in a psychiatric facility, had intended to target a music festival in the city of Ansbach but was turned away because he did not have a ticket Friebe/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police officers walk along train tracks in Wuerzburg southern Germany on 19 July, a day after a man attacked train passengers with an axe. German authorities said they had found a hand-painted IS flag among the belongings of the man, an asylum seeker from Afghanistan, who seriously injured four members of a family of tourists from Hong Kong in his rampage Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis German police killed a teenage assailant after he attacked passengers on a train in Wuerzburg, southerg Germany with an axe and a knife on 18 July, seriously wounding three people Karl-Josef Hildenbrand/AFP/Getty Images

Police said they believed the threat had been neutralised through the raids on Thursday night and Friday morning.

About 400 police officers were involved in the raids.

Mr Ashton said police had gathered unspecified evidence in the raids that the plotters were planning to use explosives in their attack.

"We gathered the makings of an improvised explosive device," Mr Ashton said.

He added: "Certainly [there was the] potential for quite a number of people to be injured or killed in this attack."

Loading....

Mr Ashton described those arrested as "self-radicalised" and inspired by Isis propaganda.

Victoria state Premier Daniel Andrews said there will be extra police on the streets of Melbourne on Christmas Day to make the public feel safe.