There were no reports of injuries, police and fire officials said, but about 30 nearby residents were temporarily evacuated.

The fire was put out around 11 a.m., the city of Naha’s fire department said.

In total, about 4,200 square meters of the facility have been destroyed, including the main, north and south buildings. All three were wooden structures, but no sprinklers were installed, the fire department said.

More than 10 fire engines were dispatched to the scene. Fire officials said it is highly likely that the fire started in the main building.

The castle long served as the heart of the Ryukyu Kingdom, which ruled the island prefecture from 1429 to 1879, but was destroyed in the Battle of Okinawa in the closing days of World War II. The structures were reconstructed in 1992, and the castle ruins were designated as a UNESCO World Heritage site in 2000.

“The cause of the fire has not been determined yet but a security company alarm went off at around 2:30 in the morning,” said Ryo Kochi, a spokesman with the Okinawa Prefectural Police.

Television footage showed large orange flames engulfing the castle.

Kochi said a tourist event was being held at the castle from Sunday, and some work linked to the event continued until 1 a.m. Thursday but it is not clear whether that was linked to the fire.

Naha Mayor Mikiko Shiroma told reporters that she is “very shocked” about the fire. “It is extremely regrettable,” she said.

“It is a World Heritage site that represents Okinawa. More than anything, I am very worried about the fact that many Naha citizens live in neighboring areas, and I have received reports that the fire might be threatening or affecting residents of the areas,” she added.

The city will make its “greatest possible efforts” to deal with the fire and its aftermath, she said.

Chief Cabinet Secretary Yoshihide Suga said at a news conference in Tokyo that the government will do all it can to reconstruct the gutted castle.

The castle uses both Japanese and Chinese architectural styles, underlining the unique characteristics of the Ryukyu Kingdom, which long served as a transportation hub connecting China and Japan.

Thanks to the faithful nature of the reconstruction, the castle was registered along with the surrounding complex and other Ryukyu sites in the region as a World Heritage Site.

“Five hundred years of Ryukyuan history (12th-17th century) are represented by this group of sites and monuments,” the entry on the UNESCO website explains. “The ruins of the castles, on imposing elevated sites, are evidence for the social structure over much of that period, while the sacred sites provide mute testimony to the rare survival of an ancient form of religion into the modern age.”

The reconstructed main hall in particular is praised in the entry as “a great monument symbolising the pride of the Ryukyu people.”

During the July 2000 summit of the Group of Eight major economies in Okinawa, leaders had dinner in the castle’s north hall.

Japan is dotted with historic castle complexes, most of which are careful reconstructions of original buildings.

Several have suffered damage from natural disasters in recent decades, including Kumamoto Castle in Kyushu, which was badly damaged by a series of devastating earthquakes.

In 1949, the main hall of Horyuji, a Buddhist temple in Nara Prefecture, burned down, and Kinkuji in Kyoto Prefecture was destroyed by arson in 1950.

Reflecting on the Horyuji fire, Japan enacted the Act on Protection of Cultural Properties in 1950. Fire drills have been carried out throughout Japan every Jan. 26, which the government designates as national fire prevention on cultural treasure day, since 1955.

Despite those preventive measures, tragedies continued to take place. Fires destroyed halls of the Kashihara Shrine in Nara Prefecture in 1993 and Todaiji Temple, also in Nara, in 1998.

In September this year, the Cultural Affairs Agency outlined fire prevention measures for national treasure sites and important cultural properties, including the placement of fire extinguishers, following the massive fire at Notre Dame Cathedral in Paris.