A bus was left damaged after a traffic cone weighted down with concrete was thrown at it from the Guild Hall.
AdvertisementPolice have issued an appeal for information after the incident which left two female passengers shaken and a woman with minor cuts to her ankle.
A gang of six teenagers, made up of four boys and two girls, are being hunted by detectives.
Police say a single decker bus was heading towards Lord Street when the cone was thrown from the balcony of the Guild Hall towards one of the side windows of the bus.
The glass was smashed in the bus window just as it was at the junction with Lancaster Road.
The incident happened around 8.15pm on Tuesday 29 July.
PC Bell of Preston Police said: “This was a reckless act which left the bus driver and the passengers very upset and shaken. Thankfully no one was seriously injured but it could have been a lot worse. I would urge anyone who may have seen this incident or who has any information about what happened to come forward and contact police on 101 quoting crime reference number DA1406377.”
Crimestoppers can also be called anonymously on 0800 555 111.