A spokesman for Alton Towers said: "On Thursday 1st September, Alton Towers Resort stopped The Smiler to investigate claims a piece of debris that had fallen from a carriage.
"At no time were guests on the ride at any risk and all were safely removed from the ride promptly by staff in line with our comprehensive standard procedures.
"As the health and safety of our guests is our priority, the ride will remain closed while the Resort's technical team investigate the matter."
Workers helped to bring those trapped down from the ride and it was then evacuated.
Writing on Facebook, Hilary Semmens said: "My son-in-law had to be harnessed off, thanks goodness my grandchildren didn't go on."
It is not the first time the rollercoaster has run into trouble.
In June last year a number of passengers were seriously injured when the rollercoaster hit a stationary car at 80km/h.
Medics were forced to work several metres in the air for hours to save the lives of those on-board.
In the US a number of amusement parks have been in the news after a series of deaths and near-misses.
Caleb Thomas Schwab, 10, died after riding the world's tallest water slide, the 17-storey Verruckt, in Kansaslast month. Caleb was "decapitated" after being flung from the ride.
In Tennessee three girls fell 12 metres to the ground after a Ferris wheel seat flipped over at a county fair.
Safety at Disney World in Orlando, Florida has also come under scrutiny after toddler Lane Graves was taken by an alligator as he and his family walked along one of the resorts beaches.
