More than a dozen drivers have been pelted with rocks and chunks of concrete thrown from freeway bridges north of Melbourne.

The rock throwers have been targeting drivers on the Hume Freeway in central Victoria since January 9, when a dozen cars were significantly damaged while driving under bridges in Broadford and Wallan.

The vandals struck again this weekend.

Six cars were hit with rocks thrown from an overpass in Wandong in the early hours of Saturday, a police spokeswoman said.

“Police are investigating and are keen to speak to any witnesses or anyone that may have seen suspicious activity in the area,” she said.

The attacks occurred between 12.10am and 12.40am with rocks thrown from the Arkells Road overpass.

While no one was injured in the incidents, previous rock-throwing attacks in Melbourne have caused serious injury and police warn it could easily kill someone.