People travelling on a train from Derby to Glasgow had to be evacuated when a fire took hold under a carriage.
The train had just left Derby station when an alarm started going off at about 13:11 BST, according to passengers.
Smoke was also reported coming from a carriage at the front of the train.
Cross Country trains confirmed there had been a "small fire underneath a carriage" and all 175 passengers were safely evacuated.
BBC journalist Dave Tracz was on board and tweeted about being guided down onto the tracks.
Matt Navarra, who was also using the service, tweeted in reply to the train firm's two-word apology: "Is that all you're going to say about my train going up in flames filling carriage with smoke and endangering my life?"
A spokesperson for Cross Country trains said: "All 175 customers on board were safely evacuated as a precaution and have already been transported back to Derby.
"As soon as it is cleared to move, the train will also return to Derby so that customers can be reunited with their luggage before we can assist them in completing their journeys.
"The train will then be moved to a nearby depot for a full technical investigation."
Other trains are taking diversions, the company said.
East Midlands Trains said services on routes to Nottingham, Derby and Matlock had been disrupted.