Screams of sheer terror: Alton Towers rollercoaster crash

The horrific accident happened just after 2pm on Tuesday when two carriages on The Smiler ride collided. The four were airlifted to hospital with horror injuries after the 50mph smash on the £18million "jinxed" ride.

One of the victims is understood to have lost a leg, it has been reported. Horrified onlookers said the coaster carnage looked like "something out of a movie".

Witnesses described the dramatic scenes as echoing horror film Final Destination and said there was "blood everywhere". The theme park, near Stoke-on-Trent, is closed today while investigations continue.

Sixteen people were in one carriage on the ride when it smashed into an empty cart on a low section of the track. Onlookers said the empty carriage had failed to get round the track on a test run – but the carriage containing riders was still sent out on a collision course.

The four whow ere rushed to hospital were two men aged 27 and 18 and two girls aged 19 and 17. All four suffered "significant crush-type lower limb injuries".

The other 12 riders - six men and six women - required medical treatment, including a man in his 20s who suffered neck and abdominal injuries.

This was the worst accident in Alton Towers' 35 year history. Dramatic footage last night emerged of the moments immediately after the crash. A person can be heard shouting: "Stop this f***ing ride!"

Eyewitness Danny Simm tweeted: "Big accident at Alton Towers, one train from The Smiler crashed into the other. "People unconscious on the ride with faces smashed in and blood everywhere… I think it will be closed for a while.

"One test cart got stuck with nobody in it but the ride operators still sent another cart with people in it round… then it crashed." Another Alton Towers visitor Jack Carver, 33, who also witnessed the aftermath of the smash, said: "It was like a horror movie hearing those screams. "There was pure terror in their voices. Both in the air and on the ground.

"It reminded me of that film Final Destination where the rollercoaster comes off the tracks. But I never thought I'd see similar in real life. "Some of the riders you could still see moving, others were still. It was really scary.

"I heard it happen and there was this ear-splitting crunch as the carriages went into each other."It must have gone into it with some speed. I will never forget that sound and I just pray everyone is alive."

And Lloyd Coller, who also was at Alton Towers for the day, said: "I didn't actually see it but I heard it. It sounded exactly like a car crash – just metal on metal." Emergency workers spent four-and-a-half hours battling to rescue the trapped victims as they dangled 25ft up in the air at a 45 degree angle.

Alton Towers has confirmed that a full investigation into the incident has been launched. But bosses have refused to put a time-frame on the theme park reopening.

Nick Varney, chief executive of Merlin Entertainments which runs the Staffordshire attraction, said a fail-safe designed to prevent the accident "didn't work the way it used to". He said: "Today we will take a more measured view of what was going on and whether it was specific to just the Smiler and take a view about opening Alton Towers.

"I and the whole team are totally devastated by what happened yesterday." He said the two carriages "should not have been on the same piece of track".

It was the second anniversary of the ride first opening on Sunday. This is not the first time the ride has been involved in an accident. In November 2013 one of the Smiler's wheels flew off and hit someone on the ride.

And in July the same year a piece of the ride fell off the track and 48 people had to be rescued. It shut again soon after this, in August, due to a "technical issue". The theme park's website says the ride is "the world's first 14 looping roller coaster."

 It is also described as "not for the faint hearted" and as featuring a "series of twisted psychological effects".The theme park has launched a hotline for people with relatives who have been affected by the incident. Anyone with concerns can call 0800 056 0154.