Four teenagers have been seriously injured after an Alton Towers roller-coaster carrying 16 people crashed into an empty carriage.
The accident happened at around 2.09pm on the Staffordshire resort's 50mph Smiler ride.
Two male and two female teenagers suffered serious leg injuries in the crash, while the other 12 occupants required triage.
A ramp was built to help emergency services reach the occupants of the ride, who were left stranded approximately 25 feet up in the air at an angle of around 45 degrees.
The £18m roller-coaster, which boasts a world record 14 loops, has been closed on two occasions because of safety concerns since opening two years ago. Following the incident, Alton Towers owner Merlin Entertainments was the biggest faller on the FTSE 100 after the crash, with its shares down 3%.
Visitors to Alton Towers reported on social media that the ride had broken down earlier yesterday.
Danny Simm, a musician and songwriter who witnessed the aftermath of the accident, said that a number of people appeared to be badly injured.
He tweeted: "People unconscious, knocked out. Blood everywhere. It really was shocking. Air ambulances landing now, people still stuck."
In July 2013, the ride was closed after reports that a bolt was seen to have fallen from the ride and in November that year, the roller-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.