A fire severely damaged Adolf Hitler’s former mountain retreat, known as the Eagle’s Nest, in the Bavarian Alps, with firefighting operations continuing on Saturday, German authorities said. A person has been detained in connection with the blaze.

The local tourism authority said the building had sustained extensive damage and it remained uncertain whether parts of the structure could be preserved.

Police said a fire alarm at the building in Germany’s southeastern Berchtesgaden district was triggered at around 9:15pm on Friday. Firefighters approaching the site, located on a cliff 1,834 metres (6,017 feet) above sea level, could see flames, according to a police statement.

The site’s difficult location made it challenging to bring fire engines to the scene. Efforts to extinguish the blaze continued on Saturday morning, police said, adding that respiratory protection equipment was required to access the building and its immediate surroundings.

Firefighters found no one inside the building, and authorities currently believe there were no injuries.

Police said a person had been detained as a possible suspect, although investigators had yet to establish whether the individual was connected to the fire.

The building, officially known as the Kehlsteinhaus, was completed in 1938. It can be reached by an elevator from the end of a winding mountain road that passes through several tunnels. The road is closed to public traffic but is used by buses transporting visitors.

Since 1952, the building has operated as a cafe and restaurant and houses an exhibition documenting its history. It was closed to visitors on Friday before the fire broke out.