Aerial footage captured by a drone shows a huge blaze that devastated the 18th century mansion Clandon Park House in Surrey on Wednesday.
Around 80 firefighters tackled the blaze at its height, which sent flames shooting into the sky with billows of dense black smoke.
Pictures: 18th century mansion devastated by blaze
The Grade-I listed property has been left a "shell" but some of its valuable historical artefacts have been saved, the National Trust's director-general said.
"It's a very upsetting sight to anyone who loved this wonderful and historic building", said Dame Helen Ghosh.
She added: "We have saved some significant items but certainly not everything that we wanted to save."
Staff and volunteers were safely evacuated when the alarm was raised just after 4pm yesterday, and structural engineers are due to visit the property later today.
Roger Childs, of Surrey Fire and Rescue Service, said the intensity of the flames burnt away floorboards and ceilings.
"The original crews on the scene had to deal with a developed fire as soon as they got to the scene. It's significantly damaged across the whole of the building."