Four people have been seriously injured in a collision between two carriages on Alton Towers’ Smiler rollercoaster.

Sixteen people were on the carriage, the other, which it hit, was empty. Staff at the theme park were on scene immediately after the incident which occurred at 14:09 BST on 2 June, while emergency crews were building a platform to reach those stranded on the ride.

Resort operator, Merlin Entertainments, said in a statement: "Emergency services were on the scene almost immediately along with the community first responders who worked closely with Resort staff to evacuate the 16 people on the ride. Everybody involved was fully evacuated by 18.35 BST and the emergency services and Alton Towers’ experienced care team were on hand to look after them. Four people with serious injuries were treated at the scene and are now in hospital. Relatives of all those involved have also been contacted."

The Smiler – the only rollercoaster in the world with 14 loops – had previously been closed on two occasions due to safety concerns, on one occasion injuring riders after some of the ride's wheels fell off.

According to reports, two men aged 27 and 18 and two females aged 19 and 17 suffered serious leg injuries in the accident and were taken by air ambulance to major trauma centres. The other 12 occupants also required medical treatment, including a man in his 20s who suffered neck and abdominal 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.

"The safety of our visitors is our primary concern. The park will remain closed until we understand better the cause of this dreadful incident. I would like to thank the emergency services for their swift and effective response – they were outstanding. A full investigation is now underway and we will continue to work closely with the emergency services and the Health and Safety Executive."