Alton Towers amusement park will remain closed today as an investigation continues into an accident on a rollercoaster that left four people with serious injuries.

Some passengers were trapped 25ft in the air for four-and-a-half hours after two carriages on the 50mph Smiler ride crashed on a low section of the track.

Two men aged 27 and 18 and two women aged 19 and 17 suffered serious leg injuries in Tuesday's accident and were airlifted to major trauma centres.

Twelve other people on the ride, six men and six women, required medical treatment, including a man in his 20s who suffered neck and abdominal injuries.

Nick Varney, chief executive of Merlin Entertainments, which runs the park, said: "It goes without saying that I and the whole team here are totally devastated and a little bit shell-shocked by what’s happened here today.

"Our thoughts are obviously with those that were injured and their families. As a company we exist to give people safe, fun and memorable days out and today something clearly went terribly wrong."

Mr Varney said the Staffordshire amusement park had "never had an accident like this".

He added that the investigation, which will involve the UK's Health and Safety Executive, will try to establish how two cars were on the same section of track at the same time, something he said should be "impossible".

Merlin's share price lost more than 3% of its value on Tuesday as news of the accident reached investors.