Photo/Illutration Visitors were able to see part of the World Heritage underground ruins through a glass portion of the floor of the Seiden main hall of Shuri-jo castle in Naha. (Provided by the Okinawa Commemorative National Government Park)

NAHA--The Oct. 31 blaze that destroyed much of Shuri-jo castle here generated mountains of debris that likely damaged some of the UNESCO World Heritage site's underground ruins.

The Okinawa Prefectural Board of Education said it will conduct an on-site investigation in conjunction with the Cultural Affairs Agency.

Board officials told a prefectural assembly education and welfare committee meeting Nov. 5 that investigators confirmed that debris from the fire had found its way into underground remains after a glass portion of floor in the now-gutted Seiden main hall was broken in the blaze.

Before the fire, visitors were able to observe part of the underground remains through the glass portion.

According to the board, columns to support the building and stone steps under the ground might have been damaged as well.

The underground remains are thought to date to before the 17th century. The area covering about 4.7 hectares, including the underground portion of the Seiden hall, was registered on UNESCO's World Heritage list in 2000 as one of the Gusuku Sites and Related Properties of the Kingdom of Ryukyu.

Except for the part that was open to the public, the remains were covered with a 60-centimeter-thick protective layer of soil when the main hall was rebuilt after the war.

As a result, board officials said those parts likely emerged unscathed from the fire.