A man who says he was a passenger on the Smiler when some of the wheels flew off has told ITV News Central of his "absolute fear".
Kevin Hayes-Heath told ITV News Central that he was in the front row of the carriage and was "bombarded by the fibre bearings which were splitting and breaking up at the highest point of the ride".
An Alton Towers spokesperson has apologised for the ride closure and says an investigation into the incident is ongoing. They say "all of the rides and attractions are expected to meet extremely high standards, technologically, mechanically and in terms of the end experience".
The Smiler ride was closed yesterday afternoon when some of its small plastic guide wheels became detached. Most were caught in the netting below the train but several hit passengers on the front row of the train.
Two were treated by park staff and all four people stayed at the park for the rest of the afternoon.
The park says:
The Smiler ride at Alton Towers is closed after some of its wheels came off yesterday afternoon.
Several people at the front of the train were hit by the wheels.
The park says a full investigation is now going on to work out when the ride can reopen.
A new 'land' is to open at Alton Towers in Staffordshire next year.
Opening in May, the five-acre CBeebies Land will have live characters and shows for pre-school aged children.
Alton Towers in Staffordshire has been forced to close its Smiler ride after reports that a bolt was seen to have dropped from the ride. Watch the rollercoaster in full swing before it was closed.
Alton Towers has been forced to close its new multi-million pound rollercoaster after reports that a bolt was seen to have dropped from the ride.
Visitors queuing for the £18m Smiler ride, which has 14 loops and reaches speeds of up to 53mph, say they saw a piece of metal break away from the ride and land near them, leaving a gap in the track.
Around 48 people had to be helped off the ride, which was then closed to allow for technical teams to investigate.
Alton Towers' new record breaking rollercoaster has opened after several delays because of technical problems.
The 14 loop ride, which cost the theme park £18 million to build, was meant to open around a week ago.
With 14 loops to the previous record of 10, it is the largest roller-coaster ever built.
Alton Towers' new record breaking roller coaster still remains closed because of teething problems.
The 14 loop ride, which cost the theme park £18 million to build, was meant to open five days ago.
For more information, head to Alton Towers' website.
Alton Towers' new record breaking rollercoaster has had its opening delayed again because of technical problems.
The 14 loop ride, which cost the theme park £18 million to build, was meant to open to the public yesterday.
However on the Staffordshire attraction's website, it says the ride is still not operational today, due to 'unforeseen teething problems'.
People who have booked tickets to specifically ride the new rollercoaster are advised they can have their tickets revalidated for another date during the season.