Fireman Mark Alderson: "On arrival we were met by multiple casualties both on the ride and at ground level"
Two carriages collided at Blackpool Pleasure Beach when one of them became jammed on the rails, police have said.
Thirty people were injured when the second carriage crashed into the back of the first car on the Big Dipper ride on Tuesday evening.
Up to 21 casualties were taken to Blackpool Victoria Hospital with facial, back and neck injuries. Among them was a seven-year-old child.
David Cam, a spokesman for The Pleasure Beach, apologised for the accident.
The ride has been closed until the investigation is completed
He said: "It's extraordinarily rare that we have an incident like this and it's very sad for us to realise that some people have been injured and we wish them well and a very speedy recovery."
The ride has been closed while the Health and Safety Executive (HSE) investigates.
After the crash, the two cars came to rest 20ft (6m) off the ground.
Firefighters rescued the riders using a specialist rope team, stretchers and spinal boards.
A Blackpool, Fylde and Wyre Hospital spokesman said: "Twenty of the 21 patients have been discharged but one of the riders, a 25-year-old man, is still in hospital and may require surgery to his face."
Removed on stretchers
Mark Alderson, station manager at South Shore fire station, said: "We started to evacuate the people that were trapped at the high level.
"These casualties were the 'walking wounded' and only had minor injuries.
"They were removed from the carriages and away from the incident to a casualty clearing station.
"The more seriously injured were stabilised in position. We then took the casualties from the ride in stretchers and down on to the ground level using specialist rope rescue equipment."
The Big Dipper was built 88 years ago
Ian Bell, head of Coaster Force, a group dedicated to rollercoasters at attraction parks, said the crash was one of the worst he had seen for two years - but that would not prevent him from going on it in the future.
He said: "It may be an old ride, but that does not mean it is not safe. The older (they are) the more checks they have - it certainly won't stop me from going on it.
"It's one of my favourite rides in Blackpool."
A spokesman for Blackpool Pleasure Beach said staff were "working closely with the emergency services and the Health and Safety Executive".
A spokesman for the HSE said its investigation was under way.
"An inspector visited the site yesterday evening and has returned today," he said.
"Specialists will be brought in to determine how the incident occurred and whether any measures need to be taken to prevent this from happening again.
"The ride remains closed while the investigation is ongoing."
The Big Dipper was constructed in 1921, has a track length of 3,295ft (1,013.9m) and has a maximum speed of 35mph (56kph).
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