Yobs threw a shopping trolley at a bus as it travelled along a busy south Manchester road.
The incident happened between 7.45pm and 8pm on Tuesday, as the 101 bus drove along the A5103 Princess Parkway.
The front top window of the double-decker bus was smashed but fortunately no one was injured.
The incident is one of a number of reported incidents where objects have been thrown at passing vehicles from the Yew Tree Lane Footbridge.
Nine incidents have been reported since the beginning of December. In most cases items such as bottles have been thrown, but after this incident police are keen track the offenders down.
Northenden Beat Manager, Police Constable Debbie Wright, said: "I cannot comprehend why anyone would think it acceptable to launch a shopping trolley at a moving vehicle.
"Thankfully no one was injured, but it is no exaggeration to say that an act such as this could result in innocent people being killed.
"Throwing any item at a moving vehicle, whether it be a bottle or something larger, is incredibly stupid and puts the lives of motorists in very real danger.
"We have had a numerous incident reported over the past few months and I would like to reassure residents we are working hard to identify the culprits.
"I believe whoever is doing this lives locally and someone will know who is responsible. I would urge anyone with any information to do the right thing and report those people to police.
"All information will be treated in strictest confidence."
Anyone with any information is asked to call Northenden police on 0161 856 4548, or the independent charity Crimestoppers, anonymously, on 0800 555 111.
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