Fire at night
The Naha city fire department says it received an emergency call reporting a fire at about 2:40 a.m. and dispatched around 30 fire trucks.
Fire department officials say the fire was mostly extinguished nine hours later. Seven buildings at the castle grounds have burned down, including the main hall and the north and south halls. They say more than 4,000 square meters of the site has been damaged. One firefighter has been taken to hospital.
Based on witness reports, police and fire officials suspect the fire began at the castle's main hall.
The castle was hosting a festival featuring the culture of the Ryukyu Kingdom. Police say staff had been preparing for one of the events until the early hours of Thursday.
What is Shuri Castle?
The castle, built about 500 years ago by the Ryukyu Dynasty, was designated a national treasure in 1933. It burned to the ground during World War Two.
The main hall was restored in 1992 and opened as a national park to mark 20 years since Okinawa reverted to Japanese rule. In 2000, it served as the venue of a banquet for leaders attending a G8 summit.
That December, remnants of the original castle were designated a UNESCO World Heritage site, along with the ruins of other castles of the Ryukyu Kingdom in Okinawa.
Okinawa's biggest industry is tourism, with people pouring in from Japan and overseas. Nearly 3 million people visited Shuri Castle Park last year, and there are concerns about how the fire will affect tourism in the prefecture.
A man who runs a company making the Okinawa liquor called awamori says, " Shuri Castle is a symbol of Japan's postwar recovery so I'm in tears. Our shop near the castle drew many tourists and the loss of it will do immeasurable damage."
Shuri Castle is supposed to play a role in next year's Olympics. The Okinawa leg of the torch relay is due to begin in the castle park next May. The organizers say they wanted to show people around the world the charm of Okinawa's ancient culture. They haven't said yet whether the fire will affect their plans.
How people reacted
Mikiko Shiroma is mayor of the city of Naha, where the castle is located. She said she's heartbroken, because the castle is a symbol of Okinawa.
Masayuki Dana, the director of Okinawa Prefectural Museum and Art Museum, was part of the team that rebuilt the castle last time. He said he cannot believe what's happened because he knows what it took to restore it. "There were no plans and no carpenters who knew the techniques from back then," he says. "So that building contained the wisdom of a great many people. I'm lost for words."
A woman who works as a crossing guard in front of the park says, "I saw the castle every day, so I'm really sad. I saw a student crying this morning. I want to know why this happened."
On social media networks, people are drawing comparisons with the fire at Notre Dame Cathedral in Paris earlier this year.
One tweet read: "I have a pain in my chest to see the castle. I understand now how the people of Paris felt when Notre Dame Cathedral burned."
Another said, "I wonder if the castle can collect donations to be rebuilt like Notre Dame Cathedral."
Police and fire department officials are looking into the cause of the fire.