Police are investigating the incident, which occurred about 1.30am Sunday. 

They are calling for any witnesses who may have seen a dark-coloured station wagon heading north along Caramut Road around that time.

First Constable Emily Durham, of Warrnambool police, said the victims were driving a 2010 Ford hatchback toward Warrnambool when the goon bag was thrown from the dark-coloured wagon near the Woodford/Tower Hill turn-offs.

The goon bag, which was believed to be full or nearly full of wine, struck the grille of the hatchback, triggering the airbags.

The inflation of the airbags resulted in the windscreen being cracked, First Constable Durham said.

She said the damage to the grille, the windscreen and the cost of resetting the airbags meant the car was a write-off.

“Both cars were travelling at 100km/h,” First Constable Durham said.

“The driver (of the damaged car) was able to pull over but it could have been quite nasty.

“This is very dangerous behaviour and it could have had an horrific outcome.

“This an almost-brand new car and it’s going to be written off. The goon bag was still stuck in the grille, so that’s how we know what happened.

“We think it was full or nearly full — there was wine splatter all over the outside of the car. It smelt of alcohol.”

First Constable Durham said anyone who saw the wagon on Caramut Road about 1.30am Sunday, or who may have been involved in a similar incident, should contact Warrnambool police.