One appliance and crew from Thame, one from Slade Park, Oxford and one from Aylesbury attended, along with three officers.
The firefighters provided assistance to South Central Ambulance Service, and released two women and one man.
Thames Valley Police, South Central Ambulance Service and the Air Ambulance were all in attendance.
The A418 was closed in both directions while the emergency Services were on the scene.
Sadly, one of the women died at the scene.
Thames Valley Police have issued a witness appeal.