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

About 4,800 square meters of the facility were destroyed by the blaze, including the main, north and south buildings. The main building was made from wood, while the north and south buildings also incorporated steel. No sprinklers had been installed, the fire department said.

 “All the (three) main buildings have burned down, and nothing remains,” said Daisuke Furugen, an official with the Naha Fire Department.

Efforts to extinguish the fire involved 30 fire engines and some 100 firefighters, he added.

Fire officials said it is highly likely the fire started inside the main building, a grand red structure with traditional tiling on the roof, and spread quickly to nearby buildings. A security company reported the fire to the fire department at around 2:40 a.m. after a fire alarm went off at around 2:30 a.m.

 Television footage showed large orange flames engulfing the castle before sunrise, with daylight fully revealing the extensive damage done to the site. In some areas little more than charred and smoking wood was left behind.

Officials said a local festival that began on Sunday was being held at the site and preparatory work linked to a portion of the event was being carried out until 1 a.m., just hours before the blaze erupted.

“We didn’t use fire,” an organization in charge of managing the castle park said of the preparatory work.

 However, it was not clear if the work was linked to the fire.

The castle long served as the heart of the Ryukyu Kingdom, which ruled 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.

“I am extremely saddened by this. I am utterly in shock,” Naha Mayor Mikiko Shiroma told reporters. “We have lost our symbol.”

 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.

Nearby residents expressed sorrow and disbelief.

“Huge flames leapt up and the adjacent building caught fire after the main building collapsed,” said Ritsuko Shiratori, 70, a nearby resident who woke to the sound of police car sirens and then watched the scene unfold from the top floor of her apartment building.

 Police cars and fire trucks gathered in front of the castle’s main gate. Nearby, police officers urged people living in the area to evacuate. “It’s shocking,” a 66-year-old man said. “All we can do now is try to restore it.”

Ikue Kamiya, 47, watched smoke rise from the site with her husband. “It’s just so sad,” she said with tears in her eyes.

The castle was constructed using 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 symbolizing 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.

And the Olympic torch relay for next year’s Tokyo Summer Games was due to pass by the site as it travels around the country ahead of the games.

 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 Kinkakuji 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, 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.