TOKYO >> Fire and police investigators inspected the burned-out ruins of Shuri Castle on Okinawa today to determine the cause of the fire that nearly destroyed the symbol of the Japanese island’s cultural heritage and history of struggle.

The fire Thursday burned down the three main halls and four nearby structures at the castle in Okinawa’s prefectural capital of Naha. It took firefighters 11 hours to extinguish the blaze.

More than 130 investigators inspected the site today, according to local officials. They believe the blaze started inside the Seiden, the castle’s centerpiece, around 2:30 a.m. when no one was around.

The late hour and the castle’s design, with a spacious wooden main hall connected to other main buildings by hallways, might have allowed the fire to spread quickly.

Shuri Castle is a UNESCO World Heritage site which dates from the 1429-1879 Ryukyu Kingdom era. The castle, burned down during World War II, was largely restored in 1992 for the 20th anniversary of Okinawa’s reversion to Japan that ended the island’s 27-year U.S. occupation. Historians and other experts had continued the restoration efforts until recently.

Many Okinawans expressed deep sorrow over the damage to the castle, which is a symbol of their cultural roots as well as the history of their struggle since the 1879 annexation by Japan.

Okinawa Gov. Denny Tamaki said his heart was broken, but expressed his determination to reconstruct the castle. Tamaki, who cut short a trip to South Korea and returned to Naha on Thursday, was in Tokyo on Friday meeting central government officials to seek their support.

Chief Cabinet Secretary Yoshihide Suga expressed his sympathy to the Okinawans, adding that the government is willing to do everything it can to help the castle’s reconstruction.

Investigators were focusing on the ruins of the Seiden hall. Video on NHK public television, taken from a helicopter, showed dozens of officials in uniforms and white helmets searching through charred debris, putting pieces into buckets for further examination.

The fate of hundreds of historic Ryukyu arts and crafts also was uncertain. Fire officials said they believe treasures displayed at the castle were mostly replicas of originals kept in safe storage elsewhere, but were trying to confirm their whereabouts.

Okinawa Churashima Foundation, which oversaw the castle, said it could not immediately confirm the status of a collection of historical artifacts kept at the castle. It said more than 1,500 items including calligraphy scrolls, lacquerware and paintings were stored there, and about 400 of them may have been in buildings that burned down, Kyodo News reported. It said most of the items were stored in heat-resistant warehouses at the castle and may have been saved, but their condition could not be examined immediately due to high temperatures.

The castle had hydrants, alarms, portable extinguishers and water outside the buildings. But there were no sprinklers installed inside the buildings, Naha fire department official Ryo Kotani said.

The fire was detected when a security guard heard an alarm, Kotani said. The blaze had engulfed the hall and spread to nearby structures when firefighters arrived about 20 minutes later.