The dramatic accident late Thursday near Melbourne saw dead and injured sheep fall onto at least two moving cars and into the paths of others.
Police said one of the vehicles rolled numerous times but the occupants were not injured.
"The truck is hanging over the overpass just above the Princes Freeway," police said in a statement.
"A number of sheep have fallen to the road below, hitting two vehicles."
Motorists described chaotic scenes.
"There was nothing we could do. They were, like, literally on top of us," one woman whose car was hit told the Melbourne Age newspaper.
"We just ran straight into them. We all screamed. I slammed on the brakes and we are so lucky. My car is an absolute write-off but the sheep, I feel so bad for them. It's horrific, it really is."
Television footage showed the truck hanging precariously off the overpass with dead sheep in the wreck and littering the road below.
Police said the crashed truck had rolled over on a bend and there did not appear to be any other vehicles involved in causing the accident. (AFP)