One of the four theme-park visitors who were seriously injured in a roller-coaster accident yesterday has reportedly lost a leg.

The group is made up of two men aged 27 and 18, and two teenage girls aged 17, and 19, but it is not yet know which individual underwent the amputation.

The accident took place at the famous Alton Towers in Staffordshire on The Smiler ride, which travels at speeds of up to 85km/h.

All four suffered “significant lower limb injuries” and were trapped in a carriage for “some time”.

For anybody concerned about relatives affected by the incident on The Smiler today please contact 0800 056 0154 for more information.

— Alton Towers Resort (@altontowers) June 2, 2015

The two-year-old attraction boasts a world-record 14 loops and cost €25m to create and build, but it has had a history of problems since being launched.

During a previous scare, 16 journalists were left stranded on The Smiler for a half an hour during a preview ride before it opened to the public in May 2013.

It took emergency services a total of five hours to cut all 16 passengers involved in the incident free from the wreckage yesterday – two were seen hanging terrified 7.5metres in the air upside down. 

Witnesses also describe seeing “blood everywhere”.

The roller-coaster ride, which lasts for a little under three minutes, had broken down earlier in the day and an empty cart was subsequently sent out for a test run.

A second cart filled with the 16 passengers then followed it – but it stalled before being catapulted from behind into the empty cart, which was also stationary at the time.

Thomas Healy, 26, a business manager at McDonald’s, told Mail Online he thought the full carriage was about to be evacuated when it stopped.

But he added: “Suddenly the carriage moved – almost as though staff hit the wrong button – and it went down the loop and then smashed into the empty carriage.

“It was horrendous. The impact was massive and the people at the front looked unconscious for a bit.

“The carriage was crushed at the front and they must have suffered leg injuries. 

“There was one guy whose head was covered in blood.”

Although the venue stayed open following the incident, Alton Towers last night tweeted that the resort will be closed today. It has also set up a helpline for those concerned about relatives or friends who may have been at the theme-park

It further said that a full investigation is now underway, and added that while The Smiler has had issues, “that’s normal for roller-coasters”.

In a statement last night, Nick Varney, chief executive of Merlin Entertainments, the parent company of Alton Towers, said: “This has been a terrible incident and a devastating day for everyone here.

“I would like to express my sincerest regret and apology to everyone who suffered injury and distress today and to their families.”