Four people were  seriously injured in a collision between two carriages on the high-speed roller coaster Smiler at Alton Towers amusement park. The Smiler coaster has had some ride incidents in the past.

The crash occurred on the two-year-old Smiler attraction on Tuesday afternoon, West Midlands ambulance service said. The accident involved two carriages – one containing 16 guests and the other empty – which came together on a low section of the track.

Witnesses described hearing a sound “like a car crash” and passengers screaming for help as they were suspended in the air.

The Smiler is a Gerstlauer Infinity Coaster and is pretty new. With 14 inversions, The Smiler holds the world record for the roller coaster with the most inversions. Its roll out was plagued with problems. The roller coaster suffered a series of setbacks and ride incidents – including one that occurred during its preview event – that delayed its official opening and resulted in high number of temporary closures. The Smiler eventually opened to the public on 31 May 2013, two months after the ride’s originally planned debut.

Initially, The Smiler was expected to make its public debut in March 2013 for the park’s opening day, but due to construction delays, the date was pushed back to 23 May 2013. The date had to be pushed back further after technical issues were encountered during testing and a ride incident occurred during its preview event that stranded riders on the lift hill. Following the incident on 22 May 2013, Alton Towers explained on their website that The Smiler would not open on the originally scheduled date due to “unforeseen teething problems.”