One female and one male senior constable and two male constables were killed. "One of the officers was only very recently in the force," Mr Ashton said. He said police would await the results of the truck driver's blood analysis while searching for the runaway driver, who he urged to hand himself in to police. Chief commissioner Graham Ashton speaks to the media at the scene of a crash that killed four police officers. Credit:Simon Schluter Officers from the homicide squad and major collision units will investigate the deaths.

"We really are still piecing together what occurred here today," Mr Ashton said. "I believe this is largest single loss of police life in one incident in the history of Victoria Police. "There's an eerie quiet down there [at the scene], everyone down there is feeling it at the moment." Police Minister Lisa Neville said at a media conference late on Wednesday night that she expected government-led tributes for the victims, beginning with flags flown at half-mast. "It is an unimaginable tragedy," Ms Neville said. "They [the victims] are Victorian heroes tonight.

"Victoria Police have done an incredible job the past few weeks. Now is the time to really thank them. "Just a thank you, a nod, a wave ... to send a strong message ... a positive message and thank police for the work that they do." Police Association Victoria Secretary Wayne Gatt said he was "absolutely floored" when he was told of the deaths, and that he had to double check that the information he received about four victims was correct. "This will be felt in every police station," Mr Gatt said. "Today four of our community paid the ultimate sacrifice for protecting all of us. "These police officers were doing something that we do 10 times, 20 times, 30 times a shift; intercepting a motor vehicle at the side of the road.

"This is the bread and butter of policing, this isn’t stuff that you go to and expect to be killed. Each and every time a police officer does that for the next little while they will have this in their mind no doubt." He said the victims included police veterans and new officers. A statement from the Police Association said it was a brutal reminder of the dangers officers faced every day while protecting the public. Loading Replay Replay video Play video Play video "The Police Association is shocked and immensely saddened by the deaths of four of our dedicated members, who were killed while protecting the community," they said.

"We mourn their loss, we grieve with their families and colleagues and we will never forget them." Aerial vision from the scene shows a large number of emergency service vehicles on site, including paramedics and fire trucks, as well as a damaged Connect Logistics semi-trailer. Footage from the crash site also shows the Porsche, covered in a blue tarp, crushed under the front end of the semi-trailer, with debris scattered in its wake for more than 100 metres. Witness Clair White, a former Victoria Police employee, drove past the crash site on her way home from work. She said she had never witnessed such an awful scene. "My heart goes out to all involved and to my special Victoria Police family."

Another witness, Dan Smith, was heading outbound on the freeway when he saw about four ambulances and one police car speed past him. He said that when he got closer to the scene he saw flashing lights and at least 12 to 14 police cars and several ambulances. Others were driving the wrong way up the inbound lanes as they raced to the scene. "The police members were sprinting from their cars," he said.

"I could see the truck and then I saw the crumpled mess of the Porsche. There appeared to be someone standing either on top of the Porsche or on the front of the truck." He said a white unmarked SUV with substantial damage was also near the truck. He said he also saw a silver highway patrol car. "Half of it was crushed, almost non-existent. It was sitting on the grass on the median," he said. The silver highway patrol car was four lanes away from the spot where the collision happened, he said.

Premier Daniel Andrews said in a statement late on Wednesday night that four officers had lost their lives in the line of duty. "And tonight, somewhere in our city, four families' hearts are breaking," the statement said. "Our hearts are breaking with them. 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.