Senior Constable Luke Lougoon said the bus was replacing a train service and was taking taking passengers to Melbourne at about 5:50pm on Saturday, when the the rock was thrown with enough force to smash through the window.

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"There were about 25 passengers on the bus at the time whose safety was endangered," he said.

"We are appealing for members of the public check any dash cam footage they may have from around that time.

"It is something we take very seriously. If it had been a bit higher and had gone through and hit the driver or a passenger there would have been a very serious risk of injury.

"At the moment we are looking for a group of about four to five young people - believed to be teenagers - who fled from the area."

Anybody with information can call Bendigo police station on 5448 1300 or Crime Stoppers on 1800 333 000.

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