No one was injured.
The cause of the fire was not immediately known.
There were no reports of injuries, but about 30 residents living nearby had to be temporarily evacuated.
"I am utterly in shock", Naha Mayor Mikiko Shiroma told reporters. "My heart is broken", he said.
"I feel so sad that the castle was gone this way after being restored", she added. A Nanden, or south temple, is almost destroyed, Kochi said. It dates from and represents the Ryukyu Kingdom, which spanned 450 years until Okinawa was integrated into Japan in 1879.
The castle lay in ruins, for many years in the post-war period, when the island was still occupied by the American forces.
The castle was registered as Japan's 11th World Heritage site in December 2000, according to the park operator. This photo was taken in October 2019. Three more trucks were dispatched 45 minutes later, followed by more calls until 53 fire trucks and 171 firefighters in all from Naha and surrounding cities and towns were on scene at 9:40 a.m., he said.
Tokyo University of Science Professor Ai Sekizawa, an expert on fire prevention, told NHK that the extensive damage occurred because the fire broke out in the middle of the night when nobody was around, delaying the initial firefighting effort.
In addition to the main hall, the Hokuden north hall and Nanden south hall were completely destroyed. "Firefighters are still battling the fire". "We release up-to-date information depending on the status confirmation", said Shurijo Castle Park Management Center in its notification.
The reconstructed main hall in particular is praised in the entry as "a great monument symbolising the pride of the Ryukyu people".
"I still can't accept this as a reality", Takara said.