She described seeing injured people lying on the grass waiting to be treated.
Children who were not badly hurt were taken to the nearby Oxhill pub where teachers met them.
They are pupils at either St Bede's in Lanchester or Tanfield Comprehensive School and are aged between 11 and 18.
Parents have been informed.
Police said the 54-year-old driver was flown to the Royal Victoria Infirmary (RVI) in Newcastle with serious injuries.
The Great North Air Ambulance Service said the 12-year-old, who attends Tanfield Comprehensive, was in a stable condition when he was handed over to hospital staff.
The other bus driver - a 27-year-old from Newton Aycliffe - suffered minor injuries and was taken to hospital.
Fire crews at the scene in Stanley. Picture: Gavin Engelbrecht
Ambulances took seven children to hospital and another 12 were taken by other means, all with minor injuries.
They were taken to the RVI, the Queen Elizabeth in Gateshead and the University Hospital of North Durham.
ABOVE AND BELOW: The driver of the double-decker bus is rushed to a waiting helicopter before being transported to Newcastle's Royal Victoria Infirmary. Picture: Gavin Engelbrecht
Superintendent Colin Williamson said: "As the investigation into this collision continues, the roads in the area remain closed and we would like to thank everyone for their patience."
Ken Ball, Durham and Darlington Fire and Rescue Service district commander for Derwentside, said the operation to free the trapped bus driver was "prolonged".
"When the first crew arrived they confirmed one driver was trapped on the yellow bus going up the hill, multiple casualties involved, the majority of which were walking wounded," he said.
"When we arrived the police were in attendance and we had to get some sort of control as there was lots of walking wounded.
"The police did an excellent job along with paramedics to get them treated.
"Our priority was then to get the driver of the yellow bus released, it was a straightforward rescue for us but it was prolonged due to the fact there was two buses in a serious entanglement."
Caroline O’Neill – head of education at Durham County Council, said: “The wellbeing of pupils is our priority and we are working very closely with both school communities to ensure all support needed is offered to the young people involved and to their families.
“We are also liaising with our partners in the police and will assist in their investigation in any way we can.
“Anyone who has any information or concerns can call 0800 096 1233 from a landline or 0207 158 0197 from mobiles.”
Headteachers from the schools affected issued the following statement:
“Understandably our school communities are shocked by what has taken place and we are supporting each other, our pupils, staff and parents and keeping them fully informed.
“Headteachers from both schools attended the scene this morning and comforted the young people involved, coordinating information to their families during what was clearly an anxious time.
“We are very mindful of the injuries suffered by some of those involved and we will continue to offer pupils our help and support.
“This will include working with the local authority to ensure specialist counselling is available to anyone who would like it.
“We would like to thank the emergency services for their professionalism and rapid response and to send our thoughts and best wishes to all those now recovering from their injuries.”
POLICE investigating this morning’s collision have appealed for the driver of a small, dark-red hatchback car to get in touch with them.
It is believed the vehicle stopped at the scene of the collision which occurred at about 8.20 this morning but then drove on.
There is no suggestion that this vehicle was in anyway involved in the collision on the A693 road but it is believed the person or people travelling in it may have seen something that could help with our enquiries.
They should contact Durham Constabulary via the non-emergency number 101 and ask to speak to the collision investigators.
Updated: Two buses carrying 50 schoolchildren crash head-on in Stanley - two airlifted to hospital
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