A driver is believed to have been airlifted to hospital and a number of passengers injured when a train hit a tractor on a level crossing.
The passenger service was 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.
One person, believed to be the tractor driver, was flown to Norfolk and Norwich Hospital, according to East Anglian Air Ambulance.
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."
Seven people were treated at the scene and six others were taken to hospital, all with non-life-threatening injuries, paramedics 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.
Passengers travelling in the Norwich area were warned to expect delays and advised to check with National Rail before setting off.