A woman has been rushed to hospital in a critical condition after suffering a cardiac arrest.
The East of England Ambulance service confirmed it was called to Hilldown Road in Gadebridge, Hemel Hempstead, at 11.19am to reports of a woman in her 50s who had collapsed.
A rapid response vehicle reached the scene within four minutes before an ambulance and Herts air ambulance arrived with assistance.
The helicopter landed in the playing fields of nearby Galley Hill Primary School and Nursery, but the woman was taken to Lister Hospital in Stevenage by land ambulance.
She was thought to be in a critical condition.
The scene was cleared by around 1pm.