An eye-witness said the theme park visitors were left sitting on the £18 million Smiler ride at the Staffordshire attraction for at least half an hour on Thursday.
A spokeswoman for the resort said there had been a “temporary stoppage” but none of the 32 people suffered any injuries.
The incident comes 15 months after a major crash on the Smiler on June 2 2015 in which five people were seriously injured
An investigation found that a computer block stopping the ride because of a stationary car on the track had been over-ridden by staff, causing the crash.
As a result, the full carriage ploughed into the rear of the empty car, leaving two women needing leg amputations.
Merlin Attractions Operations Ltd admitted a breach of health and safety rules over the incident.
Images on social media appear to show the ride in a stationary position on its way up what looks like a vertical track, with people in their seats facing up towards the sky during Thursday’s incident.
Liam Dennett, 33, from Cheltenham, was in the queue for the ride when an announcement was made about a “technical fault”.
He posted videos on Facebook showing the people stuck on the rollercoaster.
Mr Dennett told the Press Association: “The ride’s still closed now. We can see it in the distance that it’s still closed. I would say between 30 and probably 35/40 minutes that they were stuck for.”
He said he would not go on the ride after seeing what happened.
“My son still wants to go on it, but I wouldn’t go on it personally now,” he said.
An Alton Towers spokeswoman said: “On Thursday September 1, Alton Towers Resort stopped The Smiler to investigate claims a piece of debris 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 whilst the Resort’s technical team investigate the matter.”
In response to someone asking if the Smiler will be open today, Alton Towers Resort said on Twitter: “Hi, We are looking to get the Smiler up as soon as possible, keep an eye on the queue time boards around the resort for more.”