Two centimetres is all that spared a policeman shot  on Tuesday morning from death or serious injury, Detective Senior Sergeant Ron Iddles said.

The 31-year-old first constable was shot in the back of the head during a routine car intercept in front of a primary school in Melbourne's north-west at 3.40am.

He is conscious and recovering at the Royal Melbourne Hospital in a serious but stable condition after suffering head injuries.

He was shot while still in his police car after he and another member, a 30-year old male first constable, attempted to intercept a Ford Escape in Robinson Street, Moonee Ponds.

Detective Senior Sergeant Iddles, the Police Association secretary, spoke to the unharmed officer on Tuesday morning. He said that despite escaping physical injuries, the officer had been badly shaken by the ordeal and may require ongoing support.

"These two members are lucky to be alive. This could have been a double fatality," he said.

"The member who was shot, we're only talking about two centimetres and it could have been a different result."

A large section of the quiet residential street, which comes to an end at St Monica's Primary School, was cordoned off on Tuesday morning while SES crews and investigators processed and cleared the scene.

Detective Inspector Steve Clarke, from the armed crime squad, said the marked divisional van had followed the Ford to the primary school where they attempted to "block the car in."

"The car's done a U-turn and as its driven out, a single shot from a 12 gauge shotgun has been discharged, pellets have gone through the open window, injuring the first constable who was driving that van," Inspector Clarke said.

He said the first constable has been taken to the Royal Melbourne Hospital where he's being treated for non-life threatening injuries.

"He's been quite conscious and able to speak," Inspector Clarke said.

"It's really only good luck rather than good management that has resulted in our police member not being more seriously injured.

"It's really concerning, it shows how dangerous police work can be."

Police are still hunting the shooter and have yet to recover a weapon but did find a vehicle matching the make and model of the car in Hossack Avenue, an industrial precinct in Coburg North, about 15 minutes drive from the shooting.

Police started canvassing Robinson Street for witnesses as the sun began to rise on Tuesday morning.

One resident, "Bob", was woken by a "bang" and heard the sound of a car leaving, at about 3.45am.

"It was a bang ... then I heard the vehicle taking off," he said.

Bob said his late father was a police member but he wouldn't let his children join the force these days.

"It's getting worse," he said.  "I wouldn't let any of my children join the police force because it's just not on anymore."

Bob said hoons had been targeting the street in recent times and that residents have made reports to police about hoon activity.

"There's been other vehicles in this street at night doing burnouts and speeding," he said. "We've taken numbers and reported to police and they still keep coming back."

A nun, Sister Cate, said she watched paramedics arrive and later saw a man with a bandage on his head who was able to walk on his own.

"I just heard a loud bang and then a few seconds later a car drove off," she said.  "Then I saw flashing lights ... I was watching from the window and the ambulance pulled up and the paramedics got out with their bags and went down that way and then after a while a few people came back and I saw one man with a bandage on his head... he was walking."

Susanna Tribe, who was visiting her parents on Robinson Street, described how she was woken at about 5am to find the street closed off by police.

"This is my childhood home, we've just come from Adelaide to visit," she said.

"It's something that would happen in America, not here.

"Just to know that someone is out there with a gun, willing to shoot an officer through a car, its frightening, really."

Detective Senior Sergeant Iddles, said pulling over cars was the most dangerous job a police officer can do.

"Our members put on a uniform to protect community not to be a target," he said. "They both came within an inch of losing their lives and the emotional scars from this will live on forever."

Three weeks ago, Fairfax Media revealed guns were being found in cars police were pulling over every two days in Melbourne's north-west and that the area had been dubbed a "red zone" for its burgeoning "gangster culture".

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