Jockeys Jim Crowley and Freddy Tylicki have been taken to St George's Hospital in Tooting after suffering suspected spinal injuries following falls at Kempton.
Four horses fell in the 15:20 maiden fillies stakes, which resulted in two of the riders requiring medical treatment.
Steve Drowne and Ted Durcan were also thrown as a result of the pileup, but both jockeys managed to walk back to the weighing room.
"Both jockeys have gone to St George's in Tooting for further investigation," the Racing Post quotes clerk of the course Barney Clifford as saying. "Freddy Tylicki was airlifted and Jim Crowley has gone by road ambulance.
"Both are on spinal boards and both gave their consent to me and the doctor to update their next of kin family members. I can't say anymore than that at this stage.
"I touched base with Steve Drowne and he was fine. Ted Durcan was quite shaken. I just hope and pray that both Freddy and Jim are okay."
The incident caused the rest of the afternoon's racing to be abandoned.
