Rescue workers in showground alert.
The child, understood to be about 10, was thought to have stumbled on the field at Alwinton Border Shepherds' Show, in the upper Coquet Valley.
Members of the Northumberland National Park Search and Rescue Team (NNPSRT) were close by at the time, raising money for their voluntary service.
Team spokesman Richard Holmes said: "Our members were immediately on the scene and provided appropriate pain relief. St John Ambulance personnel also assisted, until Northumbria Ambulance Service was contacted and an emergency ambulance requested."
The remoteness of Alwinton and the seriousness of the girl's suspected injury meant the Great North Air Ambulance was called out.
It took several police officers and 12 rescue team members to secure the scene and provide crowd control, as well as marshalling for the helicopter to land in the centre of the busy showground.
The girl was taken by air ambulance to Newcastle General Hospital.