A 14-year-old boy suffered "significant" head injuries when he was hit by an ambulance as it answered a 999 call.
The ambulance service said the teenager was in a serious condition in hospital after the accident in Bath just after 4pm.
The spokeswoman said: "Due to the serious condition of the patient, police gave permission for the ambulance to leave the scene to take him to hospital.
"Clearly our primary concern is for the patient and his family - senior executives from South Western Ambulance Service have travelled to Bath and will offer to meet with the family," she said
"We are also ensuring the crew involved are fully supported. We are also working closely with the police to ensure the circumstances surrounding this serious incident are fully investigated."
The spokeswoman added: "At 4.01pm this afternoon, an ambulance crew responding to a 999 emergency reported to our clinical hub that they had struck a child near the junction with London Road and Snow Hill in Bath.
"They reported the child - a boy believed to be approximately 14 years old - had suffered a significant head injury.
"The patient was placed in the ambulance and taken by the crew straight to Royal United Hospital where he is now being treated."
Avon and Somerset Police said London road was closed in both directions while they investigated the crash.
