Four teenagers have been seriously injured in a rollercoaster crash at the Alton Towers theme park in the UK.

Sixteen people were riding in the carriage when it’s believed they crashed into an empty stationary carriage on the Smiler ride.

Stuck some 8 metres in the air at a 45 metre angle for several hours, rescuers managed to airlift the injured to safety, and they are now receiving treatment at Stoke and Coventry trauma units.

Eyewitnesses reported hearing a loud bang and screams when the accident occured at around 2pm local time.

The director said the accident was the most serious in the park’s history.

The Smiler ride opened in May 2013 and holds the Guinness World Record for the most loops on a rollercoaster, according to the park’s website.

The ride was closed in July of the same year after reports that a bolt fell from the track, and again in November after a plastic guard came loose.