A roller coaster car collided with an empty car Tuesday at a UK theme park, leaving four people with serious injuries, officials said.

The crash took place on “The Smiler” at Alton Towers Resort in Staffordshire.

Sixteen people were on the ride, according to a statement from the park. Everyone was evacuated, and the four with serious injuries were transported to hospitals.

A statement from the West Midlands Ambulance Service said two teenage girls and two teenage boys suffered serious leg injuries.

“This has been a terrible incident and a devastating day for everyone here. I would like to express my sincerest regret and apology to everyone who suffered injury and distress today and to their families,” said Nick Varney, chief executive of Merlin Entertainments, which operates Alton Towers.

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