An elderly woman was airlifted to hospital after a car left the M6 and crashed down an embankment near Forton Services.
The Vauxhall Corsa careered off the southbound carriageway on the sliproad at junction 33 at about 2.15pm on Monday, Lancashire Police said.
A 76-year-old man who was driving and a woman passenger in her sixties were rescued from the car by firefighters who had to remove the roof.
The North West Air Ambulance was scrambled to the scene.
Its crew flew the woman to Royal Preston Hospital.
An air ambulance spokesman said she was being treated for suspected spinal and abdominal injuries after the car hit a tree on the embankment.
Police said a dog inside the car was also injured and the RSPCA had to be called.
Lancashire Fire and Rescue Service said the animal suffered broken legs and was taken to a local vet.
Lancashire Fire and Rescue Service spokesman John Taylor said two fire crews, one each from Lancaster and Garstang, were sent to the scene at around 2.18pm after the service was called by North West Ambulance Service.
He said 16 firefighters helped to release the woman from inside the stricken vehicle.
Lancashire Fire and Rescue Service crew manager John Timperley said: “The vehicle left the motorway just south of Lancaster Services on the southbound carriageway.
“The driver was out when we got there, but we had to take the roof off to get the passenger out.
“The passenger was stretchered out of the vehicle to the air ambulance, and was subsequently taken by the air ambulance to Royal Preston Hospital.”
The accident caused traffic disruption throughout the afternoon with one lane of the M6 between junctions 33 and 32 closed until 6pm.