Police do not believe the fire that destroyed Shuri Castle, a symbol of Okinawa and a World Heritage site, was caused by arson, investigators said.

In analyzing the evidence, including security camera footage at the gutted site, police have found no traces of intrusion into the castle ahead of the fire breaking out, they said Friday.

Okinawa Churashima Foundation, which manages the castle, told a news conference on Friday that a security guard conducted a routine patrol inside the Seiden main building about an hour before the fire broke out and found nothing amiss at the time, the foundation said.

As the castle is a popular destination for visitors to Okinawa, the first weekend since the fire saw many tourists expressing disappointment.

Hitomi Takagawa, 72, from Matsuyama, Ehime Prefecture, said she was impressed by the castle’s bright red color when she visited seven years ago.

“I planned this trip because I wanted to see that again, so it’s sad,” she said.

The blaze started at around 2:30 a.m. Thursday and engulfed seven wooden buildings, including the restored buildings of the Seiden hall, the Hokuden north hall and the Nanden south hall, occupying a total of more than 4,000 square meters on a hill overlooking the prefectural capital of Naha. It was extinguished at around 1:30 p.m. after burning for about 11 hours.

There were no reports of any injuries.

The city’s fire department said the castle’s heat detectors notified them of the fire at 2:34 a.m. Thursday.

An on-the-spot investigation at the site was conducted by around 100 local police and fire department officials Friday and their probe continued Saturday.

Aside from the heat detectors and seven security cameras, no other electrical appliances were active that night, a foundation official said.

Of about 1,500 artifacts kept in the castle buildings, over 400 may have been lost, according to the foundation.

A festival recreating scenes from ancient rituals was about to enter its fifth day at the castle on the day the fire broke out.

Around 70 staff members connected to the festival had been on the premises, with workers installing lights and other equipment nearby, but they had all left by just after 1 a.m., prior to one of the security guards making his rounds.