Four police officers have been killed in a serious crash with a truck on a major Melbourne freeway on Wednesday evening.

The officers were killed when a truck ploughed through them as they stood on the Eastern Freeway dealing with a speeding Porsche driver near the Chandler Highway at Kew about 5.40pm.

The group included a female senior constable, a male senior constable and two male constables, one of whom had only recently joined the force.

The tragedy, which the homicide squad and coroner is investigating, marks the greatest number of deaths of police in a single incident in the state.

“It’s a very tragic night for Victoria Police,” chief commissioner Graham Ashton told reporters at the scene on Wednesday night.

Commissioner Ashton said two officers intercepted the Porsche that had been speeding on the freeway and called for backup when they decided to impound the vehicle, with two other members soon arriving.

Shortly after, the refrigerated truck ploughed into them.

The Porsche driver then fled the scene and is still at large.

“I strongly suggest he gets himself down to the nearest police station,” the chief commissioner said.

Earlier, the Police Association Victoria confirmed the terrible news via Twitter.

The Police Association Victoria is shocked and immensely saddened by the deaths of four of our dedicated members, who were killed while protecting the community on the Eastern Freeway this afternoon. 1/3

— TPAV (@PoliceAssocVIC) April 22, 2020

“We are providing immediate and ongoing support to the colleagues and families of those members. This is a brutally sad reminder of the danger police face in the course of their service, every minute of every shift,” the association said.

“We mourn their loss, we grieve with their families and colleagues and we will never forget them.”

A male truck driver, who experienced a “medical episode” at the scene,  has been taken to hospital under police guard with non-life-threatening injuries.

But the chief commissioner said it’s unclear exactly what unfolded.

“We don’t know at this stage what has caused him to drive that truck into our police members,” he said.

Traffic stacked up for kilometres due to a major crash on one of Melbourne’s biggest highways. Lots of emergency services on Eastern Freeway near Kew. @abcmelbourne pic.twitter.com/tv6QHDrtm1

— Emilia Terzon (@EmiliaTerzon) April 22, 2020

The freeway’s lanes are closed in both directions between Bulleen Road and the Chandler Highway.

“We urge motorists to find an alternative route and avoid the Eastern Freeway tonight,” the Department of Transport said in a statement.

Earlier,  ABC reported: “It is understood a semi-trailer has hit several cars and one car is trapped beneath the truck. There are at least 20 emergency vehicles at the scene and officials are trying to get cars to turn around across the median strip into the outbound lanes.”

Images from the site show a damaged police highway patrol car and a struck SUV near a large, white semi-trailer.

The truck appears to have Connect Logistics branding. The company has been contacted for comment.

https://twitter.com/VictoriaPolice/status/1252877105391562754

Police Association Victoria secretary Wayne Gatt said the deaths would ‘‘shock police in stations across Victoria’’.

‘‘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.’’

Police Minister Lisa Neville said the tragedy hurts the whole community, encouraging people to extend their support to the force at this time.

“Now is the time for people to really thank them,” Ms Neville said.

-with AAP