Two carriages collided at Blackpool Pleasure Beach when one of them became jammed on the rails, police have said.
Thirty people were injured when the second carriage crashed into the back of the first car on the Big Dipper ride on Tuesday evening.
Up to 21 casualties were taken to Blackpool Victoria Hospital with facial, back and neck injuries. Seven are still receiving treatment.
The ride is closed while the Health and Safety Executive investigates.
A spokesman for Blackpool Pleasure Beach said that an investigation was under way to establish the cause of the incident.
He said: "There were 32 riders in total. Seven of those are being treated in hospital this morning.
Tharks to BBC news for this info and Get will soon Big Dipper