A train was disabled at Wilmslow after metal was thrown onto the tracks.
The incident happened near to Lacey Green shortly after 9.30pm on Sunday, 12th February, as the Manchester Piccadilly service to Alderley Edge travelled through the area.
Detective Chief Inspector Malcolm McKinnon said: "It appears the train struck a bag of metal which had been thrown on the line.
"At this stage we don't know whether the bag was put on the line deliberately, but we are in the early stages of the investigation and will continue to look into the matter to determine exactly what happened.
"Thankfully, though the train was damaged and disabled, none of the passengers or staff on board were injured."
DCI McKinnon added: "Lacey Green is a residential area and I am calling on people in the area, who might have witnessed anyone behaving suspiciously, to come forward.
"But for good fortune we could have been left dealing with a much more serious incident and we are determined to work out exactly how the items came to be on the track before any other services are disrupted."
If you have information about the incident in Wilmslow please call British Transport Police on 0800 40 50 40 or Crimestoppers, anonymously, on 0800 555 111. In all calls please quote incident 439 of 12/2/12.
