Four teenagers have been seriously injured after an Alton Towers rollercoaster carriage carrying 16 people crashed into an empty one.
The accident happened at around 2pm yesterday on the 50mph Smiler ride at the resort in Staffordshire, England.
Two males and two female teenagers suffered serious leg injuries in the crash, while the other 12 occupants needed treatment in hospital.
A ramp was built to help emergency services reach the occupants of the ride, who were about 25 feet up in the air at an angle of around 45 degrees.
The €25m rollercoaster, which has a world record-breaking 14 loops, has been closed twice because of safety concerns since opening two years ago.
Visitors to Alton Towers reported on social media that the ride had broken down earlier yesterday.
"Smiler broke down when I was on it this morning and now it's crashed. Hope everyone on it is OK, saw the air ambulance arrive," tweeted Lucy Farrugia.
Sophie Underwood, who was waiting to board the ride, told the BBC: "They had made quite a few announcements to say there were technical difficulties.
"They were sending coaches around with nobody on them.
"Then they said they had sorted it out so they decided to put people on the coach."
Ms Underwood described a carriage carrying passengers crashing into another that was stationary at the top of the ride.
"It was quite scary. There was a big crash and as soon as everybody heard the crash everybody started walking back and leaving the ride," she said.
Four air ambulances rushed to the scene together with four ambulances and several senior paramedic managers.
Staffordshire Fire and Rescue said it had sent four pumps, a rescue tender, rope rescue and an aerial ladder to the incident.
In July 2013 the ride was closed after reports that a bolt was seen to have fallen from it. In November that same year the coaster was closed after plastic guard wheels came loose and hit front row riders.
In another previous scare, 16 journalists were left stranded on the Smiler for around 30 minutes during a preview ride before it opened to the public in May 2013.