Rail passengers have complained of being thrown from their seats and hit by falling luggage after a train came to a sudden stop.
The driver of the 08:20 from Newcastle to King's Cross hit the emergency brake near Peterborough, operator Lumo said.
Passenger Neuma Domingos said she had a panic attack and hurt her leg and Lumo apologised for any distress caused.
Police said 15 people had minor injuries and the Rail Accident Investigation Branch had been informed.
Lumo said all travellers had been rerouted and the train was taken out of service for safety checks with later journeys cancelled.
"Regrettably there has been a knock-on effect for passengers on the 12:09 from King's Cross and the return journey at 18:52 from Edinburgh, both of which have been cancelled," Lumo said in a statement to the BBC.
Ms Domingos was returning to London for a hospital appointment after visiting family in Newcastle.
The King's College London student told the BBC: "Everything was fine until very abruptly we started veering to the right. All things fell on the floor. I was leaning on to the woman next to me and she almost fell out of her seat.
"And then very rapidly the train swung from side to side, heavily on to the left side all the luggage fell at this point. I hit my knee, people were gasping, a couple of people cried out - it was like really bad turbulence on a plane."
She added: "I'm still pretty shocked by everything, surprised and my leg still hurts. A suitcase hit a man's head. I can't get that image out of my head. The suitcase slowly moving and then bang. It happened right in front of me."
Billie Rainer, 25, said she was left "shaken" by the incident after she caught the train from Newcastle to visit friends in the capital.
"The train was swinging from side to side as it went around the corner very fast," she told the BBC.
"I felt like a massive jolt and I was lifted out of my seat. I wasn't injured but other people were, by falling items. A woman was limping because she'd been hurt.
"The train tipped to the side a bit, then loads more. My suitcase fell to the floor and a couple of people fell off chairs.
"After the train swung from side to side it came to a massive halt and stopped at Peterborough station for an hour and a bit.
"It did feel like the train had approached the corner way too fast. It was so much worse than plane turbulence."