By Jonathan Davies
Alton Towers remains closed today (Wednesday) after a "horrific" crash on the Smiler rollercoaster.
Four people were left with serious leg injuries when an empty carriage collided with another carrying 16 people at the theme park in Staffordshire.
The other 12 passengers required minor medical treatment. Some were trapped for four-and-a-half hours at a 45 degree angle, midway through the rollercoaster ride.
Merlin Entertainments, which owns Alton Towers, saw shares drop 3% after the incident, making it the biggest faller on the FTSE 100.
Nick Varney, chief executive of Merlin Entertainments, said: "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 and to their families.
"The safety of our visitors is our primary concern. The park will remain closed until we understand better the cause of this dreadful incident."
"A full investigation is now under way and we will continue to work closely with the emergency services and the Health and Safety Executive," he added.
Visitors took to social media to give their accounts of a "loud crash" and "screaming".
The £18 million rollercoaster, which holds the record for number of loops at 14, had been closed due to technical problems earlier in the day, visitors said.
It is understood that the empty carriage failed to make a loop and came back down the track into the carriage carrying the 16 visitors at around 50mph.
An Alton Towers spokesperson said the park will hopefully be open tomorrow, and said all tickets for Wednesday will either be exchanged for another date or full refunded.