Detectives are hunting a Porsche driver who fled the scene of a horrific crash that killed four police officers in Melbourne.

The Porsche driver, who allegedly fled the scene after four police officers were killed in a horror freeway crash in Melbourne and put photos on Facebook of the “graphic” crash scene, has been arrested.

The 41-year-old driver, who police say has an extensive criminal history, handed himself in to a police station this morning and was arrested. Fleeing the scene of a crash is an indictable offence.

His arrest comes as the first officer killed in the crash has been identified as 28-year-old Constable Josh Prestney.

Mr Prestney's grandmother, Eliza Anderson, told the Herald Sun he had just begun his new road policing role after graduating from the police academy in 2019.

Speaking to reporters this morning, Victorian Police Commissioner Graham Ashton said the Porsche driver, who had been pulled over by officers before 5pm last night for speeding, had taken photos of the horrific scene before allegedly walking away from the crash site.

“We are pursuing with Facebook that there has been some images placed on Facebook that appear to have been taken by this individual at the scene, before he has left the scene,” Mr Ashton said.

“And some of those photographs were circulating last night online. So, I would ask if anyone is finding photographs online, not to further circulate them. In fact we are talking to Facebook this morning about removing those images from Facebook.”

Mr Ashton said the man’s act was “disgusting” and said the photos were “quite graphic”.

“To leave the scene is a very, very low act in my view,” he said.

“If I wasn’t wearing this uniform as Chief Commissioner I’d be using far more colourful language than this...but I need to be more dignified.”

RELATED: Horrific truck crash on Melbourne highway leaves four police officers dead

Two police officers intercepted the man’s 911 Porsche, allegedly travelling at more than 140km/h, on Melbourne’s Eastern Freeway last night.

Police also did an oral fluid test at the scene that returned a positive result for some type of drug, Mr Ashton said.

Those two officers requested back-up and when all four were standing in the emergency lane of the freeway, making the decision to impound the speeding car, the tragic smash occurred.

“A large truck, a refrigerated truck, has then driven into these four police officers”, Mr Ashton said in an emotional press conference last night.

“The truck has also made considerable contact with the Porsche.

“The driver of the Porsche we don't believe was injured but has taken it upon himself to flee the scene on foot.”

The truck’s impact caused carnage at the scene with the highway patrol car being spun into the nature strip in the middle of the Eastern Freeway and the Porsche crushed under the semi-trailer.

The freeway is closed in both directions and remains an active crime scene however police hope to open it later today.

Mr Ashton said detectives had managed to collect footage from the four officers’ body-worn cameras.

Tributes and obituaries for the four officers would come later today, he said, after family had been properly informed of their deaths.

“We will be able to piece together 99 per cent of this...and get a very good picture of exactly what happened,” he said.

A number of good samaritans, including an off-duty paramedic and off-duty doctor, stopped at the scene and tried to render first aid but the four officers were unable to be saved.

Mr Ashton confirmed this morning the truck driver had suffered some sort of medical episode and had “blacked out” after the crash.

“It's not believed he has suffered injury in the accident but has had some sort of medical episode at the scene and has been taken to hospital for medical treatment. We intend him to be there under police guard for some time.”

A warrant was executed on the truck driver’s Cranbourne home early this morning.

“What was found at those premises is still under investigation,” Mr Ashton said.

The death of the four officers is the single deadliest day for Victoria Police in history.

The four who died include a female senior constable, a male senior constable and two male constables, one of whom had only recently joined the force.

Mr Ashton said this morning their deaths had resonated throughout the state’s entire force and reminded Victorians to keep to the 40km/h speed limit when emergency services have their flashing lights on.

“No doubt police out today will be looking well over their shoulders when they make those stops,” he said.

Premier Daniel Andrews issued a message of support to the families of the four officers late last night.

“Tonight, four police officers lost their lives in the line of duty. And tonight, somewhere in our city, four families’ hearts are breaking,” he said.

“Our hearts are breaking with them. But one thing is already clear: Though we may not yet know their names – we will always call them heroes,” he said.