Alton Towers remains closed for a third day, racking up losses potentially worth millions of pounds as health and safety inspectors comb the site for clues to what caused the rollercoaster crash.
Sixteen people were injured, four seriously, when two carriages on the Smiler ride collided.
The resort has been shut to the public since the "major incident" at around 2pm on Tuesday, with the Health and Saftey Executive (HSE) on site.
The owner of the theme parked is believed to have lost just under £1.5 million in the three days since the collision - around £500,000 a day.
Witnesses said the ride had experienced technical difficulties earlier in the day, with some claiming that the empty cart involved in the crash had been on a test run when it came to stop.
Neil Craig, head of operations for HSE in the Midlands, said that a specialist team of inspectors were at the scene in Staffordshire making inquiries.
He added: "Our role is to establish the facts. We will want to determine that those responsible for operating this ride have done what the law requires. We will also ensure that if there are any lessons to be learned, they are shared as soon as possible.
"Although the investigation is in its early stages, we will take action to protect the public if we uncover evidence that could affect the safety of other rides at the park or elsewhere."
Earlier today, one of the teenagers injured in the crash said that he had been "overwhelmed" by the response to the incident.
Expressing his gratitude on Twitter, 18-year-old textile design student Joe Pugh tweeted: "So overwhelmed with the response I've had from my accident at Alton Towers, Thank you for everyone's concern."
Mr Pugh's girlfriend Leah Washington is said to have been given a blood transfusion and morphine before she passed out following the collision.
Nick Varney, chief executive of Merlin Entertainments - which runs the resort, said the park could reopen only when the investigation had concluded - but he did not give a time-frame.
Writing in the Sun, he said: "At this point, I don't know if it was a technological or a human error. We want to know if this issue is isolated to The Smiler. We can't open again until we're sure."
Four people on the ride are said to have suffered serious leg injuries - two men aged 27 and 18, and two women aged 19 and 17.
Among those on board was Vanisha Singh, 29, who was in the second row of the carriage with her mother Chanda, 49, and her sister Meera, 26.
She told the Sun there had been "technical difficulties" moments before they embarked on the ride, as several test cars were sent ahead of them.
"We finally went up and were kept at the top for 10 or 15 minutes chatting, joking that we were the guinea pigs," she said.
Describing the crash, she added: "The metal safety bar smashed into our legs. There was loads of screaming. I felt a burning sensation in my pelvis, and back and neck pain.
"It was terrifying. There was blood all over the floor because it was pouring out of their legs in the carriage and dropping down. The doctors and firemen were covered in blood as they scaled the scaffolding to treat the guys on the front row."
An Alton Towers spokesman confirmed a decision had been taken to keep the park closed, and said that guests with pre-booked tickets and those arriving at the theme park would have the choice of a full refund or an alternative dated ticket.
"Guests with pre-booked tickets have the option to use their tickets tomorrow at an alternative attraction. See website for more info," he added.
Witnesses described scenes of horror after the collision, with one victim's face covered in blood and others screaming in terror.
Jack Carver, 33, said: "It was like a horror movie hearing those screams.
"There was pure terror in their voices. It reminded me of Final Destination where the rollercoaster comes off the tracks. It was really scary."
The four people who suffered critical injuries were airlifted to major trauma centres after the 16 occupants were rescued from 25ft in the air at an angle of about 45 degrees.
Some of the occupants suffered an ordeal which lasted more than four hours, with the evacuation not complete until 6.35pm.
Since opening two years ago, the £18 million rollercoaster, which boasts a world-record 14 loops, has been closed twice because of safety concerns.
In July 2013, it was closed after reports that a bolt was seen to have fallen from the ride - and in November that year the rollercoaster was closed after plastic guard wheels came loose and hit front-row riders.
Following the accident, Merlin Entertainments was the biggest faller on the FTSE 100, with shares down 3%.
The firm, based in Poole, has run Alton Towers since buying out previous owner the Tussauds Group in May 2007.