Up to three teenagers have been arrested in relation to a Melbourne terror plot that was reportedly set to be carried out on Mother's Day.

While details of two teenagers are scant, the third - believed to be aged 17 - was arrested at his family's home in Greenvale on Friday, News Corp has reported.

Police raided the 17-year-old boy's home in Clare Boulevard on Friday afternoon, where they found a number of improvised explosive devices.

The bombs were detonated at a reserve in nearby Clare Street, police have confirmed. 

A 14-year-old boy in Sydney was also arrested in relation to the "imminent threat", News Corp has reported.

Monash University terror expert Greg Barton said the arrests seemed to be a "last minute catch" by the Australian Security Intelligence Organisation, suggesting the plot was hatched out of a dark network that was out of sight of authorities.A Facebook entry believed to have been taken from the arrested Greenvale teenager's page. Photo: Channel 9

He said the plan seemed to resemble the Boston marathon bombing, where a small number of people working closely together built explosive devices designed to create havoc in a crowded area.

"I can't recall ever seeing the bomb squad called out for what seems like a genuine threat, with devices ready to go," Professor Barton told Fairfax Media.

Authorities, it appeared, were "almost caught out", he said.

"There is a feeling from this that if they got this far, how much else out there don't we know?"

A teenager was photographed hand-cuffed and sitting in a park near the Greenvale property during Friday's raid.

​A short time later, six women emerged from the house and were escorted by police to another area.

Channel Nine has reported that the Greenvale teen's Facebook account describes Islam as the "the religion of justice". Other outlets, meanwhile, have reported that his Facebook account decries those who don't pray five times a day as not being Muslim.

The teenager is the son of a respected Syrian doctor, according to News Corp.

His uncle was quoted as saying there were no signs his nephew had been radicalised, although he had recently grown a beard.

Victoria, NSW and the Australian Federal Police have remained tight-lipped about the high-level anti-terror raid.

A neighbour, who gave his name only as Bilal, said he heard what sounded like gunshots about 12.30pm on Friday.

"They couldn't tell us nothing, they just said there were believed to be explosives in the house," he said.

Residents near Clare Boulevard described police swarming their street en masse as they searched a home and car.

A family living close to the raided house was forced to spend most of the night outside the police cordon, before being let in shortly after the first explosives were detonated at 9.40pm.

Other families were told they could stay in their houses, but were required to have all their windows and doors shut.

"All of a sudden the street became full of cops, then the bomb squad came. At the start they did not let us out of the house, but then they told everyone to leave because there was some explosive," Bilal said.

Counter-terror police have conducted their second operation in two months, with a high-level search which culminated in dramatic scenes in Melbourne’s outer north yesterday afternoon.

Residents near Clare Boulevard, Greenvale, described police swarming their street en masse as they searched a home and car. Police remained tight-lipped about the reasons for the search, part of a joint operation between the Federal Police and Victoria Police.

“All of a sudden the street became full of cops, then the bomb squad came. At the start they did not let us out of the house, but then they told everyone to leave because there was some explosive,” a neighbour, who gave his name only as Bilal, said.

He said he heard what sounded like gunshots about 12.30pm. Dozens of armed officers arrived soon after, he said.

He told Fairfax Media police said there might be explosives in the house.

A man and several women are believed to have been inside the house targeted at the time of the raids.

Two young men driving a blue Holden Astra were intercepted by police in Somerton Road, only a few kilometres from Clare Boulevard, about 4.45pm, but it was unclear if the intercept was linked to the operation.

It is unclear if the operation, believed to have started on Thursday, relates to a specific threat made against police, but Victoria Police recently upgraded security measures for officers.

A black armoured car, “massive, the size of a truck, big and black” was driving up the street, Bilal said.

Witnesses also reported seeing two men led away by police into an unmarked police car.

Officers wearing hazardous material or bomb disposal suits walked inside the house at the centre of the raids about 5.15pm.

Neighbour Nathan Sakellariou said unmarked vans and police vehicles were parked outside his house on Helmsdale Crescent, before descending on a home on the corner with Clare Boulevard about 2pm.

He said he believed police had entered the property from the back fence.

“There were Victoria Police in the divisional vans but definitely federal police in the (unmarked) vans and the Prado,” he said.

“They were masked up, you could literally only see their eyes even when they were sitting in the vans.”

“I thought it was a plumber and then all of a sudden they turn on their lights so they can go through the roadblocks.”

Police were not releasing any information to neighbours, he said.

“It looks like a normal house, there’s a basketball ring out the back.”

An SUV, parked in the driveway of a double-storey house on the corner of Helmsdale Crescent, appeared to have been ransacked. The bonnet of the car was also opened.

A man who passed through the street about 2pm described a large police presence. “I saw a lot of police officers, a lot of white vans, and detectives,” he said.

Witnesses told Channel Nine that police arrived in a heavily armed vehicle and used a loudspeaker to demand any occupants come out.

A man reportedly emerged soon after and walked into the street with his hands behind his back.

Police walked the man to nearby parkland where they sat him down.

A short time later, six women emerged from the house and were escorted by police to another area.

Police would not confirm if the operation was in relation to counter-terrorism, or which suburbs were being targeted.

“Victoria Police, in conjunction with the AFP, is conducting a police operation in the northern metropolitan area this afternoon. As this relates to an ongoing investigation, it is not appropriate to comment further,” a spokeswoman said.