Police conducted Friday's raid at the Greenvale family home after learning an attack was allegedly planned for Sunday.

Investigators leave the Greenvale home where a teenager was arrested on Friday. Credit:Meredith O'Shea

The exact target was unknown, but on Thursday, Australian Federal Police and Victoria Police decided to enter the "arrest phase" because of the "imminent danger" to the public.

"This matter has been subject to an intense investigation, especially over the last nine days. On Thursday afternoon an agreement was reached that we would resolve this matter with direct action," said Victoria Police Acting Deputy Commissioner Robert Hill.

Crude pipe bombs are designed to explode in a ball of shrapnel creating maximum damage in crowded areas.

"They were very rudimentary but that doesn't really matter because at the end of the day and explosion is an explosion," Australian Federal Police Deputy Commissioner Mike Phelan said.

Police and State Emergency Services outside the Greenvale house on Saturday. Credit:Paul Jeffers

Police don't know if there were three Mother's Day targets, one selected location, or if some of the bombs were to be used against emergency service responders.

Deputy Commissioner Mike Phelan said, "The number one priority is always community safety so if it means we have to act early to save people's lives that's indeed what we are going to do."

Bomb squad officers at the Melbourne property on Friday night. Credit:Eddie Jim

Authorities said there was no evidence the plan was linked to last month's alleged Anzac Day terror plot, and declined to comment on whether the teenager acted alone.

Police are now investigating friends and associates of the teenager, as it is considered unlikely he was acting alone.

Police descended on Clare Boulevard on Friday afternoon. Credit:Eddie Jim

Counter terrorism police around Australia have now adopted a policy of moving quickly rather than waiting to identify all suspects in any potential plot.

In the recent arrest of Melbourne teenagers over a plot to attack police on Anzac Day, raids were brought forward to thwart any possible change of date by the suspects.

Police outside the property in Greenvale on Friday night. Credit:Eddie Jim

The 17-year-old Greenvale boy, who cannot be named, is believed to have been radicalised quickly, having recently dropped out of school and spent increasing amounts of time in his bedroom on the internet.

A computer and other material were also seized from the Greenvale home.

His parents are believed to have been concerned, but unaware of the extent of his withdrawal.

Mr Hill said the suspect was from a "caring and loving family."

When heavily armed police raided the house the boy chose not to surrender but attempted to fight his way to freedom. He was quickly overwhelmed.

He has been charged with two terror related offences and has been remanded to face court on Monday.

Mr Phelan said the arrest was a "sobering reminder" to all parents of the importance of being more engaged with their children.

"It is deeply troubling to police that young people in our community are becoming so disaffected and alienated that they would consider engaging in acts such as this, " he told reporters on Saturday.

Authorities said Operation Amberd began with a report to the National Security Hotline.

"Information from the community and working with the community is important. It is usually the families and friends that are the first to know have indicators of this kind of activity," Mr Phelan said.

Premier Daniel Andrews has been regularly briefed about counter-terrorism in recent weeks, including on Friday night in the wake of the Greenvale raid.

Tuesday's state budget provided $25 million to set up a special government taskforce, enlist young role models to engage with marginalised young people, and fund programs to tackle the complex issue.

But Mr Andrews conceded that the funding "comes with a recognition that we don't truly understand what's driving young people to become disconnected from their family, their faith ... and all the values that we say define us."

"The Victorian government's highest priority is the safety of the community. This was a very serious operation. Yesterday's operation, following an intense and methodical investigation, has kept Victorians safe," he said.

In response to the raid, Prime Minister Tony Abbott said Australia still faced a very serious terrorism threat.

"The tragic truth is that there are people among us – not very many, it's true – but there are some people among us who would do us harm," he told reporters in Darwin.

But he urged Australians to keep going about their daily business and living their lives normally.

The 17-year-old boy is due to face the Childrens' Court on Monday.

Police said any decision to have the boy tried as an adult would be made by the Commonwealth Director of Public Prosecutions.

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In NSW, the Joint Counter Terrorism Team confirmed that officers attended locations in Sydney on Friday, however, they said no arrests were made and there will be no further comment on that activity.

with Chris Vedelago