Ten people, including eight children, were injured on a rollercoaster when the M & D’s theme park ride derailed.
Nine people were kept in hospital following the theme park accident in North Lanarkshire on Sunday.
Three children were left in a serious condition. The Times reported one child was in a critical condition following the accident.
Some people were trapped upside down on the ‘Tsunami’ rollercoaster, which travels up to 40mph and involves corkscrew turns and loops.
Chief Inspector, David Bruce of Police Scotland, said: "On arrival it became clear a series of five gondolas connected on a train on the Tsunami ride have detached from the rails, struck the superstructure and then struck the ground.
"They [the gondolas] fell less than 20 feet. It would appear that they have been coming round a bend and at that point it has detached.
"It's an inverted rollercoaster which means that the riders hang in gondolas below the rails rather than sit above them.”
Eye witnesses told the BBC that the car reached the first corner at high speed and didn’t turn, carrying on straight through a barrier when it came off the rail.
Police confirmed that the ride “hadn’t struck anything on the ground”.
A joint investigation is being conducted by police and the HSE.
Theme park M & D’s, located near Strathclyde Park, Motherwell, was closed following the incident.
This is not the first incident involving a ride at M & D’s. In March, eight people had to be rescued by firefighters when the park's Tornado rollercoaster ground to a halt 20 ft (6m) in the air.