Six people were taken to hospital and 23 others treated for cuts and bruises following an accident on a ride at Alton Towers.
The Runaway Mine Train ride is one of the older attractions
It happened when the front carriages of the Runaway Mine Train became separated and rolled back into the rest of the ride at the Staffordshire theme park.
The ride, which was full with 46 passengers at the time, was immediately evacuated and was closed to the public.
Alton Towers and the Health and Safety Executive are investigating the crash.
Two women, aged in their 30s or 40s, were flown by air ambulance to North Staffordshire Hospital suffering possible whiplash, spinal or abdominal injuries of the sort seen in car crashes, a Staffordshire Ambulance spokesman said.
A third woman was taken by land ambulance to the same hospital and a man is thought to have made his own way to a casualties centre in Leek.
Two other people were taken to Accident and Emergency later. It is believed all six would have left hospital on Thursday evening.
The ride is billed as "a speeding locomotive that's out of control"
The 23 others were treated at a medical centre at the theme park.
A spokeswoman for the theme park said: "The health and safety of our guests is our primary objective. The ride has been closed and will remain so whilst a thorough investigation is carried out."
The rollercoaster ride is one of the older attractions at the theme park.
Its description on the theme park's website invites customers to "rattle along the rickety rails and mine shafts, past trees and rivers, on a speeding locomotive that's out of control - and getting faster every second."
The spokeswoman said it was unclear how long the ride would be closed for. The rest of the theme park remains open.