A train has been forced to terminate at Chesterfield after "an incident in a tunnel" caused carriage windows to shatter.
One of the passengers on board the Penzance to Glasgow service said he first heard a loud "clanking" noise from under the train.
Mike Jempson said "people were getting anxious" so he raised concerns to staff.
He added shortly afterwards, something came off the train, hit the ground and sent stones flying up the windows, making them shatter.
A CrossCountry spokesman said: "Window glass did not break and there are no reported injuries on board.
"An investigation will take place to determine what caused the incident."