A driver is believed to have been seriously hurt and a number of passengers injured when a train hit a tractor on a level crossing.
The passenger service was reportedly carrying around 135 people when it crashed into the vehicle in Roudham, Norfolk.
Police, ambulance and fire services were called to the scene at around 12.30pm on Sunday.
British Transport Police said the train operator and a number of passengers were treated at the scene by paramedics.
Passenger Tom Smith posted on Twitter: "My train just crashed into a tractor on the line, thankfully no one seriously hurt on the train. Hopefully the tractor driver is ok as well."
Alex Youngs shared photos of the shattered carriage windows and passengers being evacuated on to the tracks as an emergency services helicopter circled overhead.
"Everyone seems ok, driver injured but only panic attacks reported," he wrote.
Minutes later, he posted: "Tractor driver seriously injured, otherwise injuries minor."
Passengers travelling in the Norwich area were warned to expect delays and advised to check with National Rail before setting off.
Ten patients were treated at the scene and 10 were taken to hospital, all with non-life-threatening injuries, East of England Ambulance Service said.
Four ambulances, one rapid response vehicle, the Hazardous Area Response Team, three ambulance officers and the East Anglian Air Ambulance attended, a spokesman added.