Two air ambulances were scrambled after a collision involving a double decker bus and two cars on the A607 Rearsby Bypass on Sunday afternoon.
A crew from Derbyshire Leicestershire and Rutland Air Ambulance (DLRAA) treated a woman aged in her 70s with serious injuries to her chest, torso and legs.
Medics from Warwickshire and Northamptonshire Air Ambulance (WNAA) gave treament to a man in his 80s who had potential spinal injuries.
Both were flown to Queen’s Medical Centre, in Nottingham, and the current state of their health is not known.
Emily Magdij, a spokeswoman for DLRAA, said both crews were alerted at 3.33pm and arrived at the scene within 17 minutes.
“Both services worked with two doctors from East Midlands Immediate Care Scheme, East Midlands Ambulance Service and the fire and police services,” said Ms Magdij.
“They worked with the resources at the scene to assess and treat four patients.
“DLRAA treated a woman in her 70s with serious injuries to her chest, torso and legs.
“WNAA treated a man in his 80s who had possible spinal injuries. He was given pain relief and flown to Queen’s Medical Centre as well.”
The accident happened on the Leicester-bound carriageway shortly before 3.25pm and involved a double decker bus, a grey Ford Kuga and a Ford B Max.
A spokesperson for Leicestershire Police said: “The female front seat passenger in the B Max was taken to the Queen’s Medical Centre in Nottingham, with life-threatening injuries.
“The driver of the Kuga and a front seat passenger both sustained minor injuries.
“No one on the bus was injured.”
Police are appealing for witnesses to the collision to come forward - call DC Pete Davies on the non-emergency 101 number.