Portland police Acting Sergeant Vicki Phillips said officers were called to the accident scene on the Princes Highway between Lyons Road and Greenwald Road at 4.45am.

"A truck hit a mob of cows which were on the road. Officers had to enthanise seven black cows," she said.

"The driver of the truck was not injured.

"It's cold, wet and dark at night and we would ask all drivers to take all possible care and be aware that there may be livestock or native animals on the roads.”