A man was flown to a Melbourne hospital after a two car head-on collision on the Princes Highway near Boorcan.
Victoria police Sergeant Paul Marsland said the collision occurred just after midday on Friday.
"One of the cars was towing a trailer and the two cars collided head-on," he said.
"The car towing the trailer was heading towards Warrnambool where we believe the driver lost control and veered onto the wrong side of the road.
"Three males and one female were all injured in the crash with one being flown to Melbourne with non-life threatening internal injuries.
"We are still investigating the cause of the accident but at this stage there is an indication the trailer was part of the reason control was lost."
The area around the crash on the highway has been closed and is expected to re-open later this afternoon.
An Ambulance Victoria spokeswoman said a man in his 30s was flown to a Melbourne hospital with injuries to his chest, leg and abdomen in a stable condition.
"A man in his 20s also has injuries to his back and pelvis and a woman in her 30s has injuries to her face," the spokeswoman said.
"Both have been taken to hospital by road ambulance in a stable condition."
VicRoads has advised motorists all lanes of the Princes Highway are currently closed at Boorcan Road
"Motorists should plan to avoid the area if possible and allow extra time," it said.
"The scene is under the control of Victoria Police and will re-open as soon as it safe to do so."
At the scene Terang police Senior Constable Melissa Gray said the driver of a Subaru Forester towing a trailer lost control of the vehicle and tried to regain control but veered into an oncoming Hyundai i30.
"The passenger of the Hyundai i30 was airlifted to Melbourne with non-life threatening injuries," she said.
"Three other people were taken by road ambulance to hospital."
Any witnesses are urged to contact the Terang police or Crime Stoppers
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