The Great North East Air Ambulance Service said four casualties had been flown to hospital in three helicopters.
The most seriously injured was an eight-year-old girl who suffered head injuries and was taken to the James Cook University Hospital in Middlesbrough.
The charity also took two other children to the same hospital and a third person, suffering leg injuries, was airlifted to the University Hospital of North Tees in Stockton.
The spokeswoman added: "None of the three air ambulances are returning to the accident to pick up any more casualties, so this is a good sign."
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