A 14th Century gate in the South Korean capital, Seoul, has been partly destroyed by fire in a what police believe may have been an arson attack.
Namdaemun, or the Great South Gate, was considered to be the country's greatest national treasure.
More than 100 firefighters fought the blaze which broke out late on Sunday, but the wooden structure collapsed, leaving only the stone base intact.
Two years ago it was re-opened to the public for the first time since 1907.
President-elect Lee Myung-bak visited the site on Monday, and said simply: "People's hearts will ache."
Officially called Sungnyemun or Gate of Exalted Ceremonies, the gate had served as the main entrance to the city when Seoul became Korea's capital more than 600 years ago.
It was one of the few historic monuments in a thoroughly modernised city, which had survived both the 1910-1945 Japanese occupation and the Korean war of 1950-1953.
Seoul's southern gate during the 1392-1910 Chosun Dynasty
Constructed in 1398, rebuilt in 1447 and frequently renovated
Some pillars date back to original structure
Named top "national treasure" in 1962
Opened to public in 2006
The BBC's Kevin Kim in Seoul says it was initially thought that the fire had been put out when fire crews arrived at the gate shortly after the blaze was reported.
But South Koreans were then shocked to see flames flare up at the building as they watched live images on national television.
Officials from Korea's Cultural Heritage Administration had told firefighters to proceed cautiously, meaning they could not immediately break into the area where the fire started, according to local media.
Professor Lee Su-kyung of Seoul National University of Technology told Reuters news agency the fire could have been controlled early on had the firefighters targeted the right spot.
"Someone could have gone inside the structure," he said. "I just don't understand."
The police have refused to rule out either arson or an electrical fault as a possible cause of the fire.
Yonhap news agency quoted one official as saying that disposable lighters had been found at the point where the fire is believed to have broken out.
There were also reports of a man being seen at the building shortly before the blaze was reported.
But officials said that early eyewitness accounts were "confusing".
One officer said images from security cameras reviewed by authorities had shown no suspects.
"It is heartbreaking," said Kim Duk-Il, 40, a visitor from the southern city of Daegu, as the national icon was reduced to ashes.
By morning, only the stone base was left intact
"It remained okay even during the Korean War," Mr Kim told the AFP news agency, wiping away tears. "Our pride has fallen down."
First constructed in 1398, rebuilt in 1447 and renovated several times since, Namdaemun was the oldest wooden building in Seoul.
The two-storey structure had been given the status of "National Treasure number one" in 1962.
Initial estimates say the gate will take three years to restore, at a cost of $21m.
Authorities say they have detailed plans of the gate after measuring it in 2006.
The blaze comes less than three years after fire destroyed one of the country's oldest Buddhist temples, Naksan temple, along with its prized bronze bell.