Police have detained a suspect after a fire destroyed Adolf Hitler’s German mountain retreat.

Around 200 firefighters were deployed to the Eagle’s Nest, a remote residence at the top of Obersalzberg mountain in the Bavarian Alps, but narrow access roads and the building’s isolated location hampered their efforts.

Firefighters found the Kehlsteinhaus residence “completely ablaze” when they arrived, police said. Emergency services were alerted at 9.52pm local time (8.52pm BST) after a smoke detector triggered a fire alarm.

By Saturday, the building had been destroyed, and authorities said it was unclear whether any parts could be salvaged. German media reported that the fire had been burning for more than 12 hours and that nobody had been inside.

The man who was arrested, 33, suffers from mental health issues, the German public prosecution service said. He has been admitted to a psychiatric institution.

He was stopped by police because the motorcycle he was riding had no number plate, and was found to have injuries to one of his hands that may have been caused by the fire. If convicted he could face up to a decade in prison for arson, but his mental health could be a mitigating factor.

Lisa Maier, a police spokesman, said the building was only accessible with “heavy breathing apparatus”. Firefighters were also hampered by the narrow road linking the retreat to Obersalzberg, which is usually closed to cars.

Bad weather and water shortage also made extinguishing the fire difficult. Firefighters had to stop battling the blaze for several hours for safety reasons.

Joachim Herrmann, the Bavarian interior minister, said the Eagle’s Nest, which is owned by the German state, would be rebuilt.

“Surely we can’t leave a ruin standing?” he said when asked about the building, adding there were no concrete plans yet “only 12 hours after the fire”.

He admitted that “difficult” conversations would have to be held, but added it had been a popular tourist destination for years and was also a place of remembrance.

The building was insured and the rebuilding costs would not have to be covered by the taxpayer, he said.

The Kehlsteinhaus, nicknamed the Eagle’s Nest, was built in 1938 to host dignitaries and stands close to the Berghof, Hitler’s former summer residence located further down the mountain.

Workers were forced to labour through the night during the winter of 1938 to finish the building in time for Hitler’s birthday in April 1939.

Its lavish interior included a red Italian marble fireplace presented by Benito Mussolini, the Italian dictator. Allied soldiers later chipped pieces off it as souvenirs.

Hitler visited the Eagle’s Nest at least 14 times, although it was used largely to entertain foreign guests and diplomats.

After the Second World War, the building served as an Allied command post until 1960, when it was returned to the state of Bavaria and designated a historic monument.

The nearby Berghof residence was heavily damaged in a British air raid on April 25, 1945, before retreating SS troops set it on fire days later. Its ruins were demolished in 1952 to prevent the site from becoming a shrine.