A train had to be taken out of service after it hit what police believe was a concrete block left by yobs on a railway track in Northamptonshire.
British Transport Police said the incident put lives of passengers and staff at risk and resulted in services being cancelled and others being delayed.
The incident happened near Irchester disused station on the Midland Mainline between Irchester and Rushden in Northamptonshire on Friday, 25 September at around 7pm.
PC Mike LeConte, investigating, said: “The train, the 6pm London to Melton Mowbray service, hit what we think may have been a concrete block or something similar that had been placed on the track, luckily no-one was injured but this could have been far worse.
“The air suspension on the train was damaged, and the impact of the collision caused the fire system to activate in one of the carriages to activate.”
The train had to be taken out of service at Wellingborough and the incident resulted in the cancellation of four trains and significant delays to a further eleven services.
PC LeConte added: “Incidents of this nature are, obviously, extremely serious. They pose a real threat to the life of staff and passengers, cause thousands of pounds worth of damage and result in delays to services.
“We have followed a number if lines of enquiry since the incident and have increased patrols in the area. We are now appealing for anyone with any information to come forward.
“I would urge anyone who witnessed this incident, or who has information regarding the identity of those responsible, to get in contact with us.”
Anyone with information that could assist should contact British Transport Police on 0800 40 50 40 or text 61016 quoting reference MSUB/B3 of 23/10/2015. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.