A man aged in his 40s suffered serious facial injuries after he was hit in the head with an iron bar about 10.15am at the site where a caravan overturned on the Cobden-Warrnambool Road about two hours earlier.

A spokesman for Ambulance Victoria declined to say whether the injured man was involved in the clean up of the wrecked caravan.

The man was taken to Warrnambool Base Hospital for treatment.

Earlier a mother and daughter had a lucky escape from their 4WD vehicle after the caravan it was towing flipped on the Cobden-Warrrnambool Road.

Senior Constable Mark Barby from Warrnambool police said the daughter, who was aged in her thirties, was taken to Warrnambool Base Hospital for observation but did not appear to be injured.

Senior Constable Barby said the mother, a woman aged in her fifties from the Cobden area, was uninjured.

He said the accident happened about 8.20am this morning when the pair were travelling west on the Cobden-Warrnambool Road and passed a large truck near the Ralph Illidge sanctuary at Naringal East.

The tailwind from the rear of the truck was believed to have caused the caravan to swerve from side to side across the road, Senior Constable Barby said.

The driver, the woman aged in her fifties, tried to correct the caravan's swerving and braked but the caravan flipped on to its top, flicking the 4WD around 180 degrees before it stopped alongside a large tree by the side of the road.

Senior Constable Barby said an off-duty paramedic from Geelong stopped to give assistance to the pair before an ambulance and police arrived.

Traffic flow was reduced to one lane on the Cobden-Warrnambool Road for a short distance near the accident site.