According to the West Midlands Ambulance Service, there were 16 people riding in one carriage on the attraction when the crash happened just after 2pm.
It is believed the passengers crashed into a stationary carriage which was empty at the time.
Danny Simm, who was at the theme park when the accident happened, tweeted: "People unconscious, knocked out. Blood everywhere. It really was shocking. Air ambulances landing now, people still stuck."