A drug-affected driver has been arrested more than 12 hours after fleeing the scene of a truck crash which left four Victoria Police officers dead.
The 41-year-old man, who is known to police, is being interviewed by homicide detectives on Thursday.
"Police have located the driver of a Porsche believed to be involved in the fatal collision involving the death of four police members in Kew yesterday," a police statement reads.
The police investigation into the exact cause of the collision remains ongoing and a coronial investigation into the fatal incident will start.
Coroner Darren Bracken will run the investigation and has told Victoria Police to compile a coronial brief of evidence.
The arrested man was behind the wheel of a Porsche pulled over by officers for speeding at 140km/h on the Eastern Freeway on Wednesday evening and he had tested positive to drugs.
Officers had pulled over a speeding driver in a Porsche, who tested positive for drugs. Source: AAP
More officers were called to impound the car and while all four police were standing by the side of the road, a truck ploughed into them.
The Porsche driver ran from the scene and it's alleged he took photos of the crash and shared them on social media.
Flags will fly at half-mast across Victoria on Thursday in honour of the officers who died when the truck ploughed into them as they stood on the Eastern Freeway at Kew on Wednesday.
The officers were identified on Thursday afternoon as leading senior constable Lynette Taylor, constable Glen Humphris, senior constable Kevin King, and constable Josh Prestney.
All four officers were mowed down by the refrigerated truck after it veered off the traffic lanes into the emergency lane.
Victoria Police Chief Commissioner Graham Ashton (centre) is seen near where emergency services responded to the collision. Source: AAP
"It is an unprecedented event for us to lose so many officers in one event. Officers just doing their work, just doing their job," Victoria Police Chief Commissioner Graham Ashton said Thursday.
Pulling over a car is routine work for police.
The 41-year-old Porsche driver apparently took photos at the crash site and shared them on social media, Mr Ashton told reporters.
"As a chief Commissioner, to have four officers killed last night - someone who has clearly been driving erratically on the freeway with an extensive criminal history, it disgusts me," Mr Ashton said.
"And then to leave the scene is a very, very low act in my view."
Police have since located the driver, who is now assisting with the investigation.
The truck driver had a medical episode after the crash, blacked out and is in hospital under police guard.
Victoria Police Chief Commissioner Graham Ashton speaks about the incident that killed four officers. Source: AAP
Mr Ashton said it was unclear whether he experienced the episode before or after the accident or exactly what unfolded.
Police raided the truck driver's Cranbourne home last night and are yet to reveal what they found.
Trevor, a cousin of one of the deceased officers and who drives a truck similar to the one involved in the tragedy, told Melbourne radio 3AW he was shocked by the tragedy.
"It hasn't hit home yet, but the job they do, I don't think is respected enough," he said.
Premier Daniel Andrews asked all Victorians to pause and honour Victoria Police officers for the work they do.
"To live a life in the service of others is a deeply impressive thing, to lose your life in the service and protection of others is a tragedy," he said.
"But one thing is already clear: Though we may not yet know their names - we will always call them heroes."
Police Association Victoria secretary Wayne Gatt said it was every police officer's worst nightmare to go to the scene of the death of a colleague, let alone four.
Emergency services responding to the collision near the Chandler Highway on Wednesday evening. Source: AAP
"These police officers were doing something that we do 10 times, 20 times, 30 times a shift - intercepting a motor vehicle on the side of the road, this is the bread and butter of policing," he told reporters.
"This isn't stuff that you go to do and expect to be killed doing. But each and every time a police officer does that for the next little while, they'll have this in the back of their minds, there's no doubt."
Prime Minister Scott Morrison also extended his sympathies to the loved ones of the four officers, calling it a "dark day for the police force".
"You step up every day, you stand between us and that danger every single day and we are deeply grateful for your service, deeply grateful for your sacrifice," said Mr Morrison.
More than $20,000 has been raised towards the $2 million target for the families of the deceased police officers via a GoFundMe page.
The freeway remains closed between Bulleen Road and the Chandler Highway.
