A fire has ripped through Shuri Castle, a World Heritage Site in Okinawa, Japan, destroying the main building.
Firefighters have been battling the flames since this morning. No injuries have been reported so far.
The wooden castle, built about 500 years ago in the Ryukyu Dynasty, was designated Japan's national treasure in 1933.
It was previously almost destroyed in a battle during World War Two. The current structure is a reconstruction.
The north and south buildings of the castle, of all which were wooden structures, have also burned to the ground, Japan Times reported.
"The cause of the fire has not been determined yet but a security company alarm went off at around 2.30 in the morning," Ryo Kochi, a spokesman with the Okinawa prefectural police told news agency AFP.
Shuri Castle sits on top of a hill overlooking the city of Naha, Okinawa's capital, and is surrounded by curved stone walls.
It served as a campus for Okinawa's largest public university until the 1970s, and has been a popular tourist attraction since.
The mayor of Naha said she was worried by reports that the fire could "threaten or affect" residents in surrounding areas.
Mayor Mikiko Shiroma, told national broadcaster NHK, the city would "do everything in our power" to deal with the fire and its aftermath.
According to Okinawa's tourism site, the castle burned down three times during the Ryukyu Dynasty and was burnt down again in World War Two during the Battle of Okinawa.
It is currently the largest wooden building in Okinawa.
The castle had been scheduled as a stop on the 2020 Tokyo Olympic torch relay route.