Police in the southern German state of Bavaria have detained a 33-year-old German manduring a fire at Adolf Hitler's Alpine mountain retreat, the Kehlsteinhaus, also known as the Eagle's Nest.

Dispatchers in Traunstein received a fire alarm from the building at 21:15 local time (19:15 GMT) on Friday and firefighters found it engulfed in flames.

Some 200 emergency personnel were deployed to the scene where the blaze was still burning early on Saturday, as police said difficult terrain hindered efforts to bring the fire under control.

Police said they apprehended the man riding a motorcyclenear the scene, German media reported. A criminal investigation has been launched.

There is currently nothing to suggest the involvement of further suspects, police official Gerhart Holzinger told a press conference on Saturday afternoon.

Public prosecutor Rainer Vietze said a psychiatric report had concluded the 33-year-old man showed signs of possible mental illness and diminished responsibility might therefore be assumed.

Vietze said a possible political motive was also being considered, but stressed the investigation was in its early stages.

The residence, above the town of Berchtesgaden, was one of several buildings in the area used by the Nazi dictator and his entourage during World War Two.

Hitler and top Nazi officials used his nearby Berghof residence to plan the invasion of the USSR in 1941 and the whole complex was considered one of his headquarters.

He also used the area as a backdrop for propaganda films portraying him as a lover of animals and nature.

Local media reported that site had been "largely destroyed" and the public was urged to avoid the area.

Bavaria's Interior Minister Joachim Herrmann told reporters that the site would "under no circumstances remain a ruin", broadcaster BR24 reported. "It is important that we continue our work of remembrance," he added.