The Scenic Railway was the centrepiece of Dreamland
Up to 80 firefighters have been battling a blaze which severely damaged a listed rollercoaster at the former Dreamland amusement site in Kent.
Police said they were treating the fire, which broke out on Monday afternoon at the Scenic Railway at Margate, as suspicious.
Kent Fire and Rescue Service had 12 appliances at the scene and a pall of black smoke hung over the town.
Fire investigation officers will enter the site when it is declared safe.
BBC Radio Kent reporter David Linington said the wooden rollercoaster had collapsed.
"It is devastating," said Thanet District Council leader Sandy Ezekiel.
"It is tragic - I used to go on it when I was a kid.
"To see it like this is heartbreaking."
The Grade II listed rollercoaster is believed to be one of the oldest of its kind left in the world.
"It looks like a third of the scenic railway has been completely lost and all the carriages appear to have gone, if they were in the building next door which went up," said Mr Ezekiel.
"When I arrived, the flames were 40-50ft high from the top of the ride.
"The fire brigade did a tremendous job in bringing it under control very quickly. The fire is now out and they are dampening down."
The future of the Dreamland site, which opened in 1920, is uncertain but campaigners and planners want it to become a heritage amusement park as part of a redevelopment scheme for Margate seafront.