The driver of a Porsche who allegedly fled the scene of a truck crash on Melbourne's Eastern Freeway, which killed four police officers, has been hit with multiple charges relating to the incident.

Key points: The Porsche driver, Richard Pusey, has been charged with failing to help at the scene of the crash

The Porsche driver, Richard Pusey, has been charged with failing to help at the scene of the crash Police allege he took photos of the crash scene before fleeing and posting them online

Police allege he took photos of the crash scene before fleeing and posting them online The driver of the truck that hit the officers and Porsche remains in hospital under police guard

Leading Senior Constable Lynette Taylor, Constable Glen Humphris, Senior Constable Kevin King and Constable Josh Prestney died when they were hit by a truck after pulling over the Porsche 911 for speeding on Wednesday afternoon.

The deaths of the two senior constables and two newly graduated constables is the biggest loss of officer lives in a single incident in Victoria Police history.

On Thursday morning, police alleged Porsche driver Richard Pusey was travelling at 140 kilometres per hour before the car was pulled over by police.

Late on Thursday evening police formally charged Mr Pusey, a mortgage broker, with multiple offences.

Those charges are:

Three counts of commit indictable offence while on bail

Three counts of commit indictable offence while on bail Driving speed dangerous

Driving speed dangerous Reckless conduct endangering life

Reckless conduct endangering life Fail to remain after a drug test

Fail to remain after a drug test Fail to render assistance

Fail to render assistance Fail to exchange detail

Fail to exchange detail Possessing drug of dependence

Possessing drug of dependence Destruction of evidence

Mr Pusey was remanded in custody to appear at Melbourne Magistrates' Court today.

Pusey allegedly took photos at the crash scene

Chief Commissioner Graham Ashton told a press conference on Thursday that the driver of the Porsche had tested positive for "some type of drug" after police stopped him.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 5 minutes 15 seconds 5 m Victorian Premier Daniel Andrews paid tribute to the officers who died.

He said it appeared the accused had taken photos of the scene before he fled and posted them to Facebook.

"Some of those photographs were circulating last night online," he said.

The photos have since been removed by Facebook.

Parts of the Eastern Freeway remained a crime scene on Thursday morning. ( ABC News: Kyle Harley )

Chief Commissioner Ashton said taking a photo of the crime scene was "disgusting" behaviour.

"As Chief Commissioner, to have four officers killed last night, from someone who was clearly driving erratically on the freeway … it disgusts me," he said.

Melbourne man James Tsagros posted dashcam footage to Facebook on March 21 which appeared to show the same Porsche overtaking his vehicle at high speed on the Eastern Freeway.

It is not known who was driving the Porsche on that occasion.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 13 seconds 13 s James Tsagros captured footage of the Porsche overtaking his car at high speed in March.

Mr Tsagros posted that he had reported the vehicle to police at the time and provided officers with his dashcam footage.

Truck driver suffered medical episode after crash

Chief Commissioner Ashton said the truck was travelling at 100 kph and hit the police car so hard it spun across the lanes of the freeway, coming to a stop in the median strip between the inbound and outbound lanes.

He later told ABC Radio Melbourne police believed the truck was originally travelling in the right-most lane, before it moved all the way across to the emergency lane shortly before the crash.

The truck driver remains in hospital under police guard and police were still waiting to interview him at 6:00pm on Thursday evening.

The crash is the largest loss of lives in one incident in the history of Victoria Police. ( AAP: David Crosling )

Chief Commissioner Ashton said the driver suffered a medical episode after the crash, "which seemed to involve him blacking out".

Police executed a warrant at the truck driver's Cranbourne address overnight and Chief Commissioner Ashton said "what was found at that premises is still the subject of ongoing investigation".

Highway Patrol officers had been called to impound the Porsche. ( AAP: Scott Barbour )

He said it was too early to say whether the crash appeared to have been deliberate.

The Homicide Squad and Major Collisions Investigation Unit are investigating the cause of the crash.

"There are a number of active leads and parts of this investigation that are under way," Chief Commissioner Ashton said.

A police car was flung into the middle of the freeway on impact. ( ABC News )

'The whole force is reeling'

Prime Minister Scott Morrison said he extended his "deepest sympathies and condolences to the families and the friends, the fellow serving officers, of the four police who were tragically killed".

"This is a terrible time, more broadly, but for these families and for the Victoria Police family and for police officers all over the country — and I know their families will be feeling the same way — this is just an awful tragedy," he said.

"A terribly dark day for that police force and our thoughts, our prayers, our sympathies are there for all of them, but also our thanks to police officers serving all over the country."

Police escorted the coroner's van from the crash scene. ( AAP: Scott Barbour )

He said it was a reminder of the dangers officers face 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," he said.

"And to those families who are knowing nothing other than terrible grief today, we stand with you as much as we possibly can."

Victoria Police officers and protective services officer recruits, instructors and staff at the Victoria Police Academy gave a minute's silence to honour the officers. ( Facebook: Victoria Police )

Premier Daniel Andrews paid tribute to the officers and sent his "best wishes, thoughts and prayers to the families of the officers who died keeping the rest of us safe".

He said it was a "terrible incident" made worse by the coronavirus crisis in the state.

"The whole force is reeling this morning from what has occurred last night," Chief Commissioner Ashton said.

Sorry, this audio has expired Chief Commissioner Graham Ashton told Virginia Trioli it was a dark day for Victoria Police.

"It is an unprecedented event for us to lose so many officers in one event, in one very terrible collision on the freeway.

"Officers just doing their work, doing their job, doing a duty that is performed by officers many times a day across our state and it is just a timely reminder of how tragic this police work can be at times.

"And, indeed very unexpectedly at times. The whole police family is feeling that this morning and will for many, many days to come."

Chief Commissioner Ashton said support was being provided to the families of the officers and members of the force.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 42 seconds 1 m 42 s Police Association secretary Wayne Gatt said it was an "unimaginable time".

The head of the Police Association of Victoria, Wayne Gatt, said the coronavirus physical-distancing measures would mean the "heroes" would not be able to be given the full-scale funeral they deserved.

"Every time one of our officers … every time they leave work, they are making a sacrifice, that is their personal safety," he told ABC News Breakfast.

"Last night four members made the ultimate sacrifices, we thank them for that and we know the community will thank them for the work they do each and every day."

He said police and protective services officers would still be reeling from what they were told on Wednesday and "what they have seen and witnessed".

"And still our members are at the scene, investigating this tragic, tragic, horrible event," he said.

Mourners left floral tributes at the Boroondara Police Station after the crash, but authorities urged people to pay their respects online. ( ABC News: Simon Tucci )

Emergency Services Minister Lisa Neville said it was "almost hard to believe" the tragedy.

"This is a difficult day, it's going to be many difficult days ahead, many difficult weeks ahead for Victoria Police and the families involved."

Chief Commissioner Ashton thanked the community for its support, but encouraged people to make their tributes online due to the COVID-19 crisis.

The deaths will be investigated by the coroner and the investigation into the exact cause of the collision remains ongoing.

Investigators are appealing for anyone with dashcam footage to contact Crime Stoppers on 1800 333 000.