YOBS threw stones at a train and broke one of its windows as it travelled through Hartlepool.
British Transport Police are investigating the incident which happened at 7.10am on Saturday, April 27, as the train approached Hartlepool Railway Station.
Two youths were seen throwing stones from a bridge near the station at the train bound for London Kings Cross.
PC Gary Sykes said: “The stones caused one of the windows to smash, but fortunately no one was injured and the train was able to continue its journey.”
“Officers want to speak to anyone who may have information about the incident or who may have witnessed what happened.
“Luckily there were no reported injuries to anyone onboard the train.
“But this could have resulted in a passenger or rail staff being seriously hurt.
“This type of behaviour is utterly unacceptable and I would urge anyone who has any information to please come forward.”
Anyone with information is urged to contact British Transport Police on 0800 405040 or text 61016 quoting reference B8/ NEA of 03/05/2013.
Alternatively call Crimestoppers on 0800 555111.