Two women aged in their 70s were left trapped in their car in a ditch on the B1101 near March following a two car collision.
The Magpas air ambulance was called to the scene following the crash, and the road will remain closed for ‘some time’ while emergency services remain at the scene.
The closure has been put in place at the junction with the A41 and the Saxon Way junction.
Two men - a 17-year-old and a 19-year-old - have been detained by police following the collision, but a spokeswoman for Cambridgeshire police said two others were still outstanding.
The spokeswoman said: “The crash happened at 3.15pm near the junction with Hook Lane.
“It involved a silver Renault Clio and a Green Lexus IS200.
“The Clio ended in a ditch, and two females were trapped.
“The Lexus remained on the road, and four people left the car.
“Two people have been detained.
“It is not thought the women have suffered life changing or life threatening injuries.”
A spokesman for the East of England Ambulance Service said: “A woman in her 70s had suffered a serious arm injury and was airlifted to Addenbrooke’s Hospital for further treatment.
“The second patient, also in their 70s, was taken to Peterborough City Hospital for further treatment.” Motorists are advised to avoid the area.
Anyone with information is asked to call police on 101.