Concrete block thrown on to train in Malvern
Several thousands of pounds worth of damage has been caused after a large brick or concrete block was thrown from a bridge on to a busy train.
The object dented the roof of the London Paddington to Hereford train as it passed through Malvern in Worcestershire on Saturday evening.
British Transport Police (BTP) said it was "sheer luck" it did not smash the driver's windscreen or go through the carriage roof.
Witnesses are urged to contact police.
Det Sgt Jon Rawson, of BTP, said officers received a report of an object, believed to be a large brick or piece of concrete, being thrown at the 16:22 London Paddington to Hereford service at about 19:00 GMT on Saturday.
If the item had gone through the windscreen or roof, it would have almost certainly have caused serious injuries or even a fatality, he added.
"This was an extremely foolish and dangerous act, which resulted in a train being damaged and a lucky escape for passengers and rail staff on board what was a busy train," he said.
"Throwing objects of any kind at fast moving trains is an incredibly irresponsible thing to do and we have stepped up patrols in the area to try to catch those responsible."