The three men and one woman were dealing with a Porsche in the emergency stopping lane when they were hit by a large truck.
Four police officers have been killed after they were hit by a truck on a motorway in Australia.
Two of the officers had stopped the driver of a Porsche for speeding along Melbourne’s Eastern Freeway on Wednesday evening.
After pulling the car over in an emergency stopping lane, they called for two more officers to help seize the vehicle.
The officers – two senior constables and two constables – were out of their cars when a large truck hit them.
Police said the truck had been travelling at 100kmph (62mph) and had hit the police car so hard that it spun across the road and ended up in the central reservation.
The driver of the Porsche, a 41-year-old man with what police described as an extensive criminal history, was not thought to have been injured, although his car was crushed by the truck.
Victoria Police Chief Commissioner Graham Ashton said the Porsche driver had tested positive for “some type of drug” after being stopped by the officers.
The man also appeared to have posted “quite graphic” photos online of the crash scene before leaving the area which police had asked Facebook to remove, Mr Ashton said.
After initially fleeing the scene, he made contact with the police and is expected to hand himself in later.
The truck driver, who blacked out after the crash, is in hospital under police guard but his injuries are not life-threatening.
His home was searched and he will be interviewed and tested to see if he was under the influence of drugs or alcohol.
Mr Ashton said the incident was the largest loss of lives in one incident in the history of Victoria Police.
In comments reported by the Australian Broadcasting Corp, he said: “Our thoughts and prayers are with the families of our officers tonight.”
He described it as a “tragedy…for the families of those officers (and) a tragedy for the whole force”.
The officers, including a female senior constable and a recent recruit, were described as “heroes” by the state premier Daniel Andrews.
He said: “We grieve alongside them – just as we grieve with every member of Victoria Police and every member of our emergency services family.
“In the coming days, formal investigations will tell us why – how – this could possibly have happened.
“But one thing is already clear: Though we may not yet know their names – we will always call them heroes.”
A man named only as Trevor from Melbourne, told radio station 3AW that his cousin was one of the officers killed in the crash.
The officer had been in the force for eight years and was married, he said, adding: “It hasn’t hit home just yet”.