Four children had to be treated for carbon monoxide inhalation after being poisoned by fumes on a school bus.
The youngsters fell ill while travelling to Hamond's High School in Swaffham, Norfolk. The bus pulled over in nearby Beachamwell.
Lorna Marsh, spokeswoman for East of England Ambulance Service, said two were taken to the Queen Elizabeth Hospital in King's Lynn for treatment while the others were treated by paramedics.
She added: "Crews in two rapid response vehicles and two ambulances assessed the casualties on scene before taking two of them to hospital.
"They were fully alert but having breathing difficulties.
"The rest of the children continued their journey to school."