Four people have received medical attention after a second Alton Towers rollercoaster collision in less than a month.
The customers were taken to the Staffordshire theme park's medical centre as a precaution after a shunt on the Sonic Spinball ride.
Officials said the two carriages "nudged each other at walking pace".
"The guests on the two cars walked off and we advised that they attend our medical centre as a precautionary measure," a spokesman for Alton Towers said.
"The ride reopened shortly afterwards."
Onlooker Danny Robinson, 24, from Liverpool, claimed Tuesday's incident happened at "full pace".
He told the Daily Mirror: "I was stood with the bags watching them when it happened.
"The carriage came round to the end at full pace and crashed into one with a young family inside. The mum in the other carriage was screaming.
"Two of my friends hit the back of their heads and another two hurt their necks. They spent about 20 minutes getting them out of the carriage.
"All four were taken to the medical centre and spent two-and-a-half hours getting checked over and heat pads on their necks.
"Afterwards one of them started throwing up everywhere and ended up going to hospital."
The passengers involved were a 36-year-old man and three women aged 33, 30 and 22, the paper said.
On Thursday, Alton Towers apologised after customers were stranded on a monorail on the hottest day of the year - but denied reports that others were stuck upside down on its Air ride.
Around 80 passengers were stranded for an hour on the monorail train in sweltering temperatures of 28C (82F).
A statement said the stoppage was caused by a "technical issue" and that passengers were kept fully informed and given refreshments.
Guests at the park were also left in mid-air on the park's Air ride in another incident on Wednesday.
Pictures on social media appear to show people stuck in a horizontal position facing the ground, but the park said reports they were left dangling upside down are completely inaccurate.
Alton Towers called it a "minor technical stoppage" that was resolved within 20 minutes and "within standard operating procedures".
The park has been in the spotlight after a crash on its Smiler ride on 2 June left five people seriously injured.
Two people, Vicky Balch, 20, and 17-year-old Leah Washington, had legs amputated after the ride collided with an empty carriage